1List::MoreUtils(3)    User Contributed Perl Documentation   List::MoreUtils(3)
2
3
4

NAME

6       List::MoreUtils - Provide the stuff missing in List::Util
7

SYNOPSIS

9           # import specific functions
10
11           use List::MoreUtils qw(any uniq);
12
13           if ( any { /foo/ } uniq @has_duplicates ) {
14               # do stuff
15           }
16
17           # import everything
18
19           use List::MoreUtils ':all';
20
21           # import by API
22
23           # has "original" any/all/none/notall behavior
24           use List::MoreUtils ':like_0.22';
25           # 0.22 + bsearch
26           use List::MoreUtils ':like_0.24';
27           # has "simplified" any/all/none/notall behavior + (n)sort_by
28           use List::MoreUtils ':like_0.33';
29

DESCRIPTION

31       List::MoreUtils provides some trivial but commonly needed functionality
32       on lists which is not going to go into List::Util.
33
34       All of the below functions are implementable in only a couple of lines
35       of Perl code. Using the functions from this module however should give
36       slightly better performance as everything is implemented in C. The
37       pure-Perl implementation of these functions only serves as a fallback
38       in case the C portions of this module couldn't be compiled on this
39       machine.
40

EXPORTS

42   Default behavior
43       Nothing by default. To import all of this module's symbols use the
44       ":all" tag.  Otherwise functions can be imported by name as usual:
45
46           use List::MoreUtils ':all';
47
48           use List::MoreUtils qw{ any firstidx };
49
50       Because historical changes to the API might make upgrading
51       List::MoreUtils difficult for some projects, the legacy API is
52       available via special import tags.
53
54   Like version 0.22 (last release with original API)
55       This API was available from 2006 to 2009, returning undef for empty
56       lists on "all"/"any"/"none"/"notall":
57
58           use List::MoreUtils ':like_0.22';
59
60       This import tag will import all functions available as of version 0.22.
61       However, it will import "any_u" as "any", "all_u" as "all", "none_u" as
62       "none", and "notall_u" as "notall".
63
64   Like version 0.24 (first incompatible change)
65       This API was available from 2010 to 2011.  It changed the return value
66       of "none" and added the "bsearch" function.
67
68           use List::MoreUtils ':like_0.24';
69
70       This import tag will import all functions available as of version 0.24.
71       However it will import "any_u" as "any", "all_u" as "all", and
72       "notall_u" as "notall".  It will import "none" as described in the
73       documentation below (true for empty list).
74
75   Like version 0.33 (second incompatible change)
76       This API was available from 2011 to 2014. It is widely used in several
77       CPAN modules and thus it's closest to the current API.  It changed the
78       return values of "any", "all", and "notall".  It added the "sort_by"
79       and "nsort_by" functions and the "distinct" alias for "uniq".  It
80       omitted "bsearch".
81
82           use List::MoreUtils ':like_0.33';
83
84       This import tag will import all functions available as of version 0.33.
85       Note: it will not import "bsearch" for consistency with the 0.33 API.
86

FUNCTIONS

88   Junctions
89       Treatment of an empty list
90
91       There are two schools of thought for how to evaluate a junction on an
92       empty list:
93
94       •   Reduction to an identity (boolean)
95
96       •   Result is undefined (three-valued)
97
98       In the first case, the result of the junction applied to the empty list
99       is determined by a mathematical reduction to an identity depending on
100       whether the underlying comparison is "or" or "and".  Conceptually:
101
102                           "any are true"      "all are true"
103                           --------------      --------------
104           2 elements:     A || B || 0         A && B && 1
105           1 element:      A || 0              A && 1
106           0 elements:     0                   1
107
108       In the second case, three-value logic is desired, in which a junction
109       applied to an empty list returns "undef" rather than true or false
110
111       Junctions with a "_u" suffix implement three-valued logic.  Those
112       without are boolean.
113
114       all BLOCK LIST
115
116       all_u BLOCK LIST
117
118       Returns a true value if all items in LIST meet the criterion given
119       through BLOCK. Sets $_ for each item in LIST in turn:
120
121         print "All values are non-negative"
122           if all { $_ >= 0 } ($x, $y, $z);
123
124       For an empty LIST, "all" returns true (i.e. no values failed the
125       condition) and "all_u" returns "undef".
126
127       Thus, "all_u(@list)" is equivalent to "@list ? all(@list) : undef".
128
129       Note: because Perl treats "undef" as false, you must check the return
130       value of "all_u" with "defined" or you will get the opposite result of
131       what you expect.
132
133       any BLOCK LIST
134
135       any_u BLOCK LIST
136
137       Returns a true value if any item in LIST meets the criterion given
138       through BLOCK. Sets $_ for each item in LIST in turn:
139
140         print "At least one non-negative value"
141           if any { $_ >= 0 } ($x, $y, $z);
142
143       For an empty LIST, "any" returns false and "any_u" returns "undef".
144
145       Thus, "any_u(@list)" is equivalent to "@list ? any(@list) : undef".
146
147       none BLOCK LIST
148
149       none_u BLOCK LIST
150
151       Logically the negation of "any". Returns a true value if no item in
152       LIST meets the criterion given through BLOCK. Sets $_ for each item in
153       LIST in turn:
154
155         print "No non-negative values"
156           if none { $_ >= 0 } ($x, $y, $z);
157
158       For an empty LIST, "none" returns true (i.e. no values failed the
159       condition) and "none_u" returns "undef".
160
161       Thus, "none_u(@list)" is equivalent to "@list ? none(@list) : undef".
162
163       Note: because Perl treats "undef" as false, you must check the return
164       value of "none_u" with "defined" or you will get the opposite result of
165       what you expect.
166
167       notall BLOCK LIST
168
169       notall_u BLOCK LIST
170
171       Logically the negation of "all". Returns a true value if not all items
172       in LIST meet the criterion given through BLOCK. Sets $_ for each item
173       in LIST in turn:
174
175         print "Not all values are non-negative"
176           if notall { $_ >= 0 } ($x, $y, $z);
177
178       For an empty LIST, "notall" returns false and "notall_u" returns
179       "undef".
180
181       Thus, "notall_u(@list)" is equivalent to "@list ? notall(@list) :
182       undef".
183
184       one BLOCK LIST
185
186       one_u BLOCK LIST
187
188       Returns a true value if precisely one item in LIST meets the criterion
189       given through BLOCK. Sets $_ for each item in LIST in turn:
190
191           print "Precisely one value defined"
192               if one { defined($_) } @list;
193
194       Returns false otherwise.
195
196       For an empty LIST, "one" returns false and "one_u" returns "undef".
197
198       The expression "one BLOCK LIST" is almost equivalent to "1 == true
199       BLOCK LIST", except for short-cutting.  Evaluation of BLOCK will
200       immediately stop at the second true value.
201
202   Transformation
203       apply BLOCK LIST
204
205       Applies BLOCK to each item in LIST and returns a list of the values
206       after BLOCK has been applied. In scalar context, the last element is
207       returned.  This function is similar to "map" but will not modify the
208       elements of the input list:
209
210         my @list = (1 .. 4);
211         my @mult = apply { $_ *= 2 } @list;
212         print "\@list = @list\n";
213         print "\@mult = @mult\n";
214         __END__
215         @list = 1 2 3 4
216         @mult = 2 4 6 8
217
218       Think of it as syntactic sugar for
219
220         for (my @mult = @list) { $_ *= 2 }
221
222       insert_after BLOCK VALUE LIST
223
224       Inserts VALUE after the first item in LIST for which the criterion in
225       BLOCK is true. Sets $_ for each item in LIST in turn.
226
227         my @list = qw/This is a list/;
228         insert_after { $_ eq "a" } "longer" => @list;
229         print "@list";
230         __END__
231         This is a longer list
232
233       insert_after_string STRING VALUE LIST
234
235       Inserts VALUE after the first item in LIST which is equal to STRING.
236
237         my @list = qw/This is a list/;
238         insert_after_string "a", "longer" => @list;
239         print "@list";
240         __END__
241         This is a longer list
242
243       pairwise BLOCK ARRAY1 ARRAY2
244
245       Evaluates BLOCK for each pair of elements in ARRAY1 and ARRAY2 and
246       returns a new list consisting of BLOCK's return values. The two
247       elements are set to $a and $b.  Note that those two are aliases to the
248       original value so changing them will modify the input arrays.
249
250         @a = (1 .. 5);
251         @b = (11 .. 15);
252         @x = pairwise { $a + $b } @a, @b;     # returns 12, 14, 16, 18, 20
253
254         # mesh with pairwise
255         @a = qw/a b c/;
256         @b = qw/1 2 3/;
257         @x = pairwise { ($a, $b) } @a, @b;    # returns a, 1, b, 2, c, 3
258
259       mesh ARRAY1 ARRAY2 [ ARRAY3 ... ]
260
261       zip ARRAY1 ARRAY2 [ ARRAY3 ... ]
262
263       Returns a list consisting of the first elements of each array, then the
264       second, then the third, etc, until all arrays are exhausted.
265
266       Examples:
267
268         @x = qw/a b c d/;
269         @y = qw/1 2 3 4/;
270         @z = mesh @x, @y;         # returns a, 1, b, 2, c, 3, d, 4
271
272         @a = ('x');
273         @b = ('1', '2');
274         @c = qw/zip zap zot/;
275         @d = mesh @a, @b, @c;   # x, 1, zip, undef, 2, zap, undef, undef, zot
276
277       "zip" is an alias for "mesh".
278
279       zip6
280
281       zip_unflatten
282
283       Returns a list of arrays consisting of the first elements of each
284       array, then the second, then the third, etc, until all arrays are
285       exhausted.
286
287         @x = qw/a b c d/;
288         @y = qw/1 2 3 4/;
289         @z = zip6 @x, @y;         # returns [a, 1], [b, 2], [c, 3], [d, 4]
290
291         @a = ('x');
292         @b = ('1', '2');
293         @c = qw/zip zap zot/;
294         @d = zip6 @a, @b, @c;     # [x, 1, zip], [undef, 2, zap], [undef, undef, zot]
295
296       "zip_unflatten" is an alias for "zip6".
297
298       listcmp ARRAY0 ARRAY1 [ ARRAY2 ... ]
299
300       Returns an associative list of elements and every id of the list it was
301       found in. Allows easy implementation of @a & @b, @a | @b, @a ^ @b and
302       so on.  Undefined entries in any given array are skipped.
303
304         my @a = qw(one two three four five six seven eight nine ten eleven twelve thirteen);
305         my @b = qw(two three five seven eleven thirteen seventeen);
306         my @c = qw(one one two three five eight thirteen twentyone);
307         my %cmp = listcmp @a, @b, @c; # returns (one => [0, 2], two => [0, 1, 2], three => [0, 1, 2], four => [0], ...)
308
309         my @seq = (1, 2, 3);
310         my @prim = (undef, 2, 3, 5);
311         my @fib = (1, 1, 2);
312         my %cmp = listcmp @seq, @prim, @fib;
313         # returns ( 1 => [0, 2], 2 => [0, 1, 2], 3 => [0, 1], 5 => [1] )
314
315       arrayify LIST[,LIST[,LIST...]]
316
317       Returns a list consisting of each element of given arrays. Recursive
318       arrays are flattened, too.
319
320         @a = (1, [[2], 3], 4, [5], 6, [7], 8, 9);
321         @l = arrayify @a;         # returns 1, 2, 3, 4, 5, 6, 7, 8, 9
322
323       uniq LIST
324
325       distinct LIST
326
327       Returns a new list by stripping duplicate values in LIST by comparing
328       the values as hash keys, except that undef is considered separate from
329       ''.  The order of elements in the returned list is the same as in LIST.
330       In scalar context, returns the number of unique elements in LIST.
331
332         my @x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 1 2 3 5 4
333         my $x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 5
334         # returns "Mike", "Michael", "Richard", "Rick"
335         my @n = distinct "Mike", "Michael", "Richard", "Rick", "Michael", "Rick"
336         # returns "A8", "", undef, "A5", "S1"
337         my @s = distinct "A8", "", undef, "A5", "S1", "A5", "A8"
338         # returns "Giulia", "Giulietta", undef, "", 156, "GTA", "GTV", 159, "Brera", "4C"
339         my @w = uniq "Giulia", "Giulietta", undef, "", 156, "GTA", "GTV", 159, "Brera", "4C", "Giulietta", "Giulia"
340
341       "distinct" is an alias for "uniq".
342
343       RT#49800 can be used to give feedback about this behavior.
344
345       singleton LIST
346
347       Returns a new list by stripping values in LIST occurring more than once
348       by comparing the values as hash keys, except that undef is considered
349       separate from ''.  The order of elements in the returned list is the
350       same as in LIST.  In scalar context, returns the number of elements
351       occurring only once in LIST.
352
353         my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5
354
355       duplicates LIST
356
357       Returns a new list by stripping values in LIST occurring less than
358       twice by comparing the values as hash keys, except that undef is
359       considered separate from ''.  The order of elements in the returned
360       list is the same as in LIST.  In scalar context, returns the number of
361       elements occurring more than once in LIST.
362
363         my @y = duplicates 1,1,2,4,7,2,3,4,6,9; #returns 1,2,4
364
365       frequency LIST
366
367       Returns an associative list of distinct values and the corresponding
368       frequency.
369
370         my @f = frequency values %radio_nrw; # returns (
371         #  'Deutschlandfunk (DLF)' => 9, 'WDR 3' => 10,
372         #  'WDR 4' => 11, 'WDR 5' => 14, 'WDR Eins Live' => 14,
373         #  'Deutschlandradio Kultur' => 8,...)
374
375       occurrences LIST
376
377       Returns a new list of frequencies and the corresponding values from
378       LIST.
379
380         my @o = occurrences ((1) x 3, (2) x 4, (3) x 2, (4) x 7, (5) x 2, (6) x 4);
381         #  @o = (undef, undef, [3, 5], [1], [2, 6], undef, undef, [4]);
382
383       mode LIST
384
385       Returns the modal value of LIST. In scalar context, just the modal
386       value is returned, in list context all probes occurring modal times are
387       returned, too.
388
389         my @m = mode ((1) x 3, (2) x 4, (3) x 2, (4) x 7, (5) x 2, (6) x 4, (7) x 3, (8) x 7);
390         #  @m = (7, 4, 8) - bimodal LIST
391
392       slide BLOCK LIST
393
394       The function "slide" operates on pairs of list elements like:
395
396         my @s = slide { "$a and $b" } (0..3);
397         # @s = ("0 and 1", "1 and 2", "2 and 3")
398
399       The idea behind this function is a kind of magnifying glass that is
400       moved along a list and calls "BLOCK" every time the next list item is
401       reached.
402
403   Partitioning
404       after BLOCK LIST
405
406       Returns a list of the values of LIST after (and not including) the
407       point where BLOCK returns a true value. Sets $_ for each element in
408       LIST in turn.
409
410         @x = after { $_ % 5 == 0 } (1..9);    # returns 6, 7, 8, 9
411
412       after_incl BLOCK LIST
413
414       Same as "after" but also includes the element for which BLOCK is true.
415
416       before BLOCK LIST
417
418       Returns a list of values of LIST up to (and not including) the point
419       where BLOCK returns a true value. Sets $_ for each element in LIST in
420       turn.
421
422       before_incl BLOCK LIST
423
424       Same as "before" but also includes the element for which BLOCK is true.
425
426       part BLOCK LIST
427
428       Partitions LIST based on the return value of BLOCK which denotes into
429       which partition the current value is put.
430
431       Returns a list of the partitions thusly created. Each partition created
432       is a reference to an array.
433
434         my $i = 0;
435         my @part = part { $i++ % 2 } 1 .. 8;   # returns [1, 3, 5, 7], [2, 4, 6, 8]
436
437       You can have a sparse list of partitions as well where non-set
438       partitions will be undef:
439
440         my @part = part { 2 } 1 .. 10;            # returns undef, undef, [ 1 .. 10 ]
441
442       Be careful with negative values, though:
443
444         my @part = part { -1 } 1 .. 10;
445         __END__
446         Modification of non-creatable array value attempted, subscript -1 ...
447
448       Negative values are only ok when they refer to a partition previously
449       created:
450
451         my @idx  = ( 0, 1, -1 );
452         my $i    = 0;
453         my @part = part { $idx[$i++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
454
455       samples COUNT LIST
456
457       Returns a new list containing COUNT random samples from LIST. Is
458       similar to "shuffle" in List::Util, but stops after COUNT.
459
460         @r  = samples 10, 1..10; # same as shuffle
461         @r2 = samples 5, 1..10; # gives 5 values from 1..10;
462
463   Iteration
464       each_array ARRAY1 ARRAY2 ...
465
466       Creates an array iterator to return the elements of the list of arrays
467       ARRAY1, ARRAY2 throughout ARRAYn in turn.  That is, the first time it
468       is called, it returns the first element of each array.  The next time,
469       it returns the second elements.  And so on, until all elements are
470       exhausted.
471
472       This is useful for looping over more than one array at once:
473
474         my $ea = each_array(@a, @b, @c);
475         while ( my ($a, $b, $c) = $ea->() )   { .... }
476
477       The iterator returns the empty list when it reached the end of all
478       arrays.
479
480       If the iterator is passed an argument of '"index"', then it returns the
481       index of the last fetched set of values, as a scalar.
482
483       each_arrayref LIST
484
485       Like each_array, but the arguments are references to arrays, not the
486       plain arrays.
487
488       natatime EXPR, LIST
489
490       Creates an array iterator, for looping over an array in chunks of $n
491       items at a time.  (n at a time, get it?).  An example is probably a
492       better explanation than I could give in words.
493
494       Example:
495
496         my @x = ('a' .. 'g');
497         my $it = natatime 3, @x;
498         while (my @vals = $it->())
499         {
500           print "@vals\n";
501         }
502
503       This prints
504
505         a b c
506         d e f
507         g
508
509       slideatatime STEP, WINDOW, LIST
510
511       Creates an array iterator, for looping over an array in chunks of
512       "$windows-size" items at a time.
513
514       The idea behind this function is a kind of magnifying glass (finer
515       controllable compared to "slide") that is moved along a list.
516
517       Example:
518
519         my @x = ('a' .. 'g');
520         my $it = slideatatime 2, 3, @x;
521         while (my @vals = $it->())
522         {
523           print "@vals\n";
524         }
525
526       This prints
527
528         a b c
529         c d e
530         e f g
531         g
532
533   Searching
534       firstval BLOCK LIST
535
536       first_value BLOCK LIST
537
538       Returns the first element in LIST for which BLOCK evaluates to true.
539       Each element of LIST is set to $_ in turn. Returns "undef" if no such
540       element has been found.
541
542       "first_value" is an alias for "firstval".
543
544       onlyval BLOCK LIST
545
546       only_value BLOCK LIST
547
548       Returns the only element in LIST for which BLOCK evaluates to true.
549       Sets $_ for each item in LIST in turn. Returns "undef" if no such
550       element has been found.
551
552       "only_value" is an alias for "onlyval".
553
554       lastval BLOCK LIST
555
556       last_value BLOCK LIST
557
558       Returns the last value in LIST for which BLOCK evaluates to true. Each
559       element of LIST is set to $_ in turn. Returns "undef" if no such
560       element has been found.
561
562       "last_value" is an alias for "lastval".
563
564       firstres BLOCK LIST
565
566       first_result BLOCK LIST
567
568       Returns the result of BLOCK for the first element in LIST for which
569       BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
570       Returns "undef" if no such element has been found.
571
572       "first_result" is an alias for "firstres".
573
574       onlyres BLOCK LIST
575
576       only_result BLOCK LIST
577
578       Returns the result of BLOCK for the first element in LIST for which
579       BLOCK evaluates to true. Sets $_ for each item in LIST in turn. Returns
580       "undef" if no such element has been found.
581
582       "only_result" is an alias for "onlyres".
583
584       lastres BLOCK LIST
585
586       last_result BLOCK LIST
587
588       Returns the result of BLOCK for the last element in LIST for which
589       BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
590       Returns "undef" if no such element has been found.
591
592       "last_result" is an alias for "lastres".
593
594       indexes BLOCK LIST
595
596       Evaluates BLOCK for each element in LIST (assigned to $_) and returns a
597       list of the indices of those elements for which BLOCK returned a true
598       value. This is just like "grep" only that it returns indices instead of
599       values:
600
601         @x = indexes { $_ % 2 == 0 } (1..10);   # returns 1, 3, 5, 7, 9
602
603       firstidx BLOCK LIST
604
605       first_index BLOCK LIST
606
607       Returns the index of the first element in LIST for which the criterion
608       in BLOCK is true. Sets $_ for each item in LIST in turn:
609
610         my @list = (1, 4, 3, 2, 4, 6);
611         printf "item with index %i in list is 4", firstidx { $_ == 4 } @list;
612         __END__
613         item with index 1 in list is 4
614
615       Returns "-1" if no such item could be found.
616
617       "first_index" is an alias for "firstidx".
618
619       onlyidx BLOCK LIST
620
621       only_index BLOCK LIST
622
623       Returns the index of the only element in LIST for which the criterion
624       in BLOCK is true. Sets $_ for each item in LIST in turn:
625
626           my @list = (1, 3, 4, 3, 2, 4);
627           printf "uniqe index of item 2 in list is %i", onlyidx { $_ == 2 } @list;
628           __END__
629           unique index of item 2 in list is 4
630
631       Returns "-1" if either no such item or more than one of these has been
632       found.
633
634       "only_index" is an alias for "onlyidx".
635
636       lastidx BLOCK LIST
637
638       last_index BLOCK LIST
639
640       Returns the index of the last element in LIST for which the criterion
641       in BLOCK is true. Sets $_ for each item in LIST in turn:
642
643         my @list = (1, 4, 3, 2, 4, 6);
644         printf "item with index %i in list is 4", lastidx { $_ == 4 } @list;
645         __END__
646         item with index 4 in list is 4
647
648       Returns "-1" if no such item could be found.
649
650       "last_index" is an alias for "lastidx".
651
652   Sorting
653       sort_by BLOCK LIST
654
655       Returns the list of values sorted according to the string values
656       returned by the KEYFUNC block or function. A typical use of this may be
657       to sort objects according to the string value of some accessor, such as
658
659         sort_by { $_->name } @people
660
661       The key function is called in scalar context, being passed each value
662       in turn as both $_ and the only argument in the parameters, @_. The
663       values are then sorted according to string comparisons on the values
664       returned.  This is equivalent to
665
666         sort { $a->name cmp $b->name } @people
667
668       except that it guarantees the name accessor will be executed only once
669       per value.  One interesting use-case is to sort strings which may have
670       numbers embedded in them "naturally", rather than lexically.
671
672         sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
673
674       This sorts strings by generating sort keys which zero-pad the embedded
675       numbers to some level (9 digits in this case), helping to ensure the
676       lexical sort puts them in the correct order.
677
678       nsort_by BLOCK LIST
679
680       Similar to sort_by but compares its key values numerically.
681
682       qsort BLOCK ARRAY
683
684       This sorts the given array in place using the given compare code.
685       Except for tiny compare code like "$a <=> $b", qsort is much faster
686       than Perl's "sort" depending on the version.
687
688       Compared 5.8 and 5.26:
689
690         my @rl;
691         for(my $i = 0; $i < 1E6; ++$i) { push @rl, rand(1E5) }
692         my $idx;
693
694         sub ext_cmp { $_[0] <=> $_[1] }
695
696         cmpthese( -60, {
697             'qsort' => sub {
698                 my @qrl = @rl;
699                 qsort { ext_cmp($a, $b) } @qrl;
700                 $idx = bsearchidx { ext_cmp($_, $rl[0]) } @qrl
701             },
702             'reverse qsort' => sub {
703                 my @qrl = @rl;
704                 qsort { ext_cmp($b, $a) } @qrl;
705                 $idx = bsearchidx { ext_cmp($rl[0], $_) } @qrl
706             },
707             'sort' => sub {
708                 my @srl = @rl;
709                 @srl = sort { ext_cmp($a, $b) } @srl;
710                 $idx = bsearchidx { ext_cmp($_, $rl[0]) } @srl
711             },
712             'reverse sort' => sub {
713                 my @srl = @rl;
714                 @srl = sort { ext_cmp($b, $a) } @srl;
715                 $idx = bsearchidx { ext_cmp($rl[0], $_) } @srl
716             },
717         });
718
719       5.8 results
720
721                         s/iter  reverse sort          sort reverse qsort         qsort
722         reverse sort    6.21            --           -0%           -8%          -10%
723         sort            6.19            0%            --           -7%          -10%
724         reverse qsort   5.73            8%            8%            --           -2%
725         qsort           5.60           11%           11%            2%            --
726
727       5.26 results
728
729                       s/iter  reverse sort          sort reverse qsort         qsort
730         reverse sort    4.54            --           -0%          -96%          -96%
731         sort            4.52            0%            --          -96%          -96%
732         reverse qsort  0.203         2139%         2131%            --          -19%
733         qsort          0.164         2666%         2656%           24%            --
734
735       Use it where external data sources might have to be compared (think of
736       Unix::Statgrab "tables").
737
738       "qsort" is available from List::MoreUtils::XS only. It's insane to
739       maintain a wrapper around Perl's sort nor having a pure Perl
740       implementation. One could create a flip-book in same speed as PP runs a
741       qsort.
742
743   Searching in sorted Lists
744       bsearch BLOCK LIST
745
746       Performs a binary search on LIST which must be a sorted list of values.
747       BLOCK must return a negative value if the current element (stored in
748       $_) is smaller, a positive value if it is bigger and zero if it
749       matches.
750
751       Returns a boolean value in scalar context. In list context, it returns
752       the element if it was found, otherwise the empty list.
753
754       bsearchidx BLOCK LIST
755
756       bsearch_index BLOCK LIST
757
758       Performs a binary search on LIST which must be a sorted list of values.
759       BLOCK must return a negative value if the current element (stored in
760       $_) is smaller, a positive value if it is bigger and zero if it
761       matches.
762
763       Returns the index of found element, otherwise "-1".
764
765       "bsearch_index" is an alias for "bsearchidx".
766
767       lower_bound BLOCK LIST
768
769       Returns the index of the first element in LIST which does not compare
770       less than val. Technically it's the first element in LIST which does
771       not return a value below zero when passed to BLOCK.
772
773         @ids = (1, 1, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 6, 7, 7, 7, 8, 8, 9, 9, 9, 9, 9, 11, 13, 13, 13, 17);
774         $lb = lower_bound { $_ <=> 2 } @ids; # returns 2
775         $lb = lower_bound { $_ <=> 4 } @ids; # returns 10
776
777       lower_bound has a complexity of O(log n).
778
779       upper_bound BLOCK LIST
780
781       Returns the index of the first element in LIST which does not compare
782       greater than val. Technically it's the first element in LIST which does
783       not return a value below or equal to zero when passed to BLOCK.
784
785         @ids = (1, 1, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 6, 7, 7, 7, 8, 8, 9, 9, 9, 9, 9, 11, 13, 13, 13, 17);
786         $lb = upper_bound { $_ <=> 2 } @ids; # returns 4
787         $lb = upper_bound { $_ <=> 4 } @ids; # returns 14
788
789       upper_bound has a complexity of O(log n).
790
791       equal_range BLOCK LIST
792
793       Returns a pair of indices containing the lower_bound and the
794       upper_bound.
795
796   Operations on sorted Lists
797       binsert BLOCK ITEM LIST
798
799       bsearch_insert BLOCK ITEM LIST
800
801       Performs a binary search on LIST which must be a sorted list of values.
802       BLOCK must return a negative value if the current element (stored in
803       $_) is smaller, a positive value if it is bigger and zero if it
804       matches.
805
806       ITEM is inserted at the index where the ITEM should be placed (based on
807       above search). That means, it's inserted before the next bigger
808       element.
809
810         @l = (2,3,5,7);
811         binsert { $_ <=> 4 }  4, @l; # @l = (2,3,4,5,7)
812         binsert { $_ <=> 6 } 42, @l; # @l = (2,3,4,42,7)
813
814       You take care that the inserted element matches the compare result.
815
816       bremove BLOCK LIST
817
818       bsearch_remove BLOCK LIST
819
820       Performs a binary search on LIST which must be a sorted list of values.
821       BLOCK must return a negative value if the current element (stored in
822       $_) is smaller, a positive value if it is bigger and zero if it
823       matches.
824
825       The item at the found position is removed and returned.
826
827         @l = (2,3,4,5,7);
828         bremove { $_ <=> 4 }, @l; # @l = (2,3,5,7);
829
830   Counting and calculation
831       true BLOCK LIST
832
833       Counts the number of elements in LIST for which the criterion in BLOCK
834       is true.  Sets $_ for  each item in LIST in turn:
835
836         printf "%i item(s) are defined", true { defined($_) } @list;
837
838       false BLOCK LIST
839
840       Counts the number of elements in LIST for which the criterion in BLOCK
841       is false.  Sets $_ for each item in LIST in turn:
842
843         printf "%i item(s) are not defined", false { defined($_) } @list;
844
845       reduce_0 BLOCK LIST
846
847       Reduce LIST by calling BLOCK in scalar context for each element of
848       LIST.  $a contains the progressional result and is initialized with 0.
849       $b contains the current processed element of LIST and $_ contains the
850       index of the element in $b.
851
852       The idea behind reduce_0 is summation (addition of a sequence of
853       numbers).
854
855       reduce_1 BLOCK LIST
856
857       Reduce LIST by calling BLOCK in scalar context for each element of
858       LIST.  $a contains the progressional result and is initialized with 1.
859       $b contains the current processed element of LIST and $_ contains the
860       index of the element in $b.
861
862       The idea behind reduce_1 is product of a sequence of numbers.
863
864       reduce_u BLOCK LIST
865
866       Reduce LIST by calling BLOCK in scalar context for each element of
867       LIST.  $a contains the progressional result and is uninitialized.  $b
868       contains the current processed element of LIST and $_ contains the
869       index of the element in $b.
870
871       This function has been added if one might need the extra of the index
872       value but need an individual initialization.
873
874       Use with caution: In most cases "reduce" in List::Util will do the job
875       better.
876
877       minmax LIST
878
879       Calculates the minimum and maximum of LIST and returns a two element
880       list with the first element being the minimum and the second the
881       maximum. Returns the empty list if LIST was empty.
882
883       The "minmax" algorithm differs from a naive iteration over the list
884       where each element is compared to two values being the so far
885       calculated min and max value in that it only requires 3n/2 - 2
886       comparisons. Thus it is the most efficient possible algorithm.
887
888       However, the Perl implementation of it has some overhead simply due to
889       the fact that there are more lines of Perl code involved. Therefore,
890       LIST needs to be fairly big in order for "minmax" to win over a naive
891       implementation. This limitation does not apply to the XS version.
892
893       minmaxstr LIST
894
895       Computes the minimum and maximum of LIST using string compare and
896       returns a two element list with the first element being the minimum and
897       the second the maximum. Returns the empty list if LIST was empty.
898
899       The implementation is similar to "minmax".
900

ENVIRONMENT

902       When "LIST_MOREUTILS_PP" is set, the module will always use the pure-
903       Perl implementation and not the XS one. This environment variable is
904       really just there for the test-suite to force testing the Perl
905       implementation, and possibly for reporting of bugs. I don't see any
906       reason to use it in a production environment.
907

MAINTENANCE

909       The maintenance goal is to preserve the documented semantics of the
910       API; bug fixes that bring actual behavior in line with semantics are
911       allowed.  New API functions may be added over time.  If a backwards
912       incompatible change is unavoidable, we will attempt to provide support
913       for the legacy API using the same export tag mechanism currently in
914       place.
915
916       This module attempts to use few non-core dependencies. Non-core
917       configuration and testing modules will be bundled when reasonable; run-
918       time dependencies will be added only if they deliver substantial
919       benefit.
920

CONTRIBUTING

922       While contributions are appreciated, a contribution should not cause
923       more effort for the maintainer than the contribution itself saves (see
924       Open Source Contribution Etiquette
925       <http://tirania.org/blog/archive/2010/Dec-31.html>).
926
927       To get more familiar where help could be needed - see
928       List::MoreUtils::Contributing.
929

BUGS

931       There is a problem with a bug in 5.6.x perls. It is a syntax error to
932       write things like:
933
934           my @x = apply { s/foo/bar/ } qw{ foo bar baz };
935
936       It has to be written as either
937
938           my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz';
939
940       or
941
942           my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/;
943
944       Perl 5.5.x and Perl 5.8.x don't suffer from this limitation.
945
946       If you have a functionality that you could imagine being in this
947       module, please drop me a line. This module's policy will be less strict
948       than List::Util's when it comes to additions as it isn't a core module.
949
950       When you report bugs, it would be nice if you could additionally give
951       me the output of your program with the environment variable
952       "LIST_MOREUTILS_PP" set to a true value. That way I know where to look
953       for the problem (in XS, pure-Perl or possibly both).
954

SUPPORT

956       Bugs should always be submitted via the CPAN bug tracker.
957
958       You can find documentation for this module with the perldoc command.
959
960           perldoc List::MoreUtils
961
962       You can also look for information at:
963
964       •   RT: CPAN's request tracker
965
966           <https://rt.cpan.org/Dist/Display.html?Name=List-MoreUtils>
967
968       •   AnnoCPAN: Annotated CPAN documentation
969
970           <http://annocpan.org/dist/List-MoreUtils>
971
972       •   CPAN Ratings
973
974           <http://cpanratings.perl.org/dist/List-MoreUtils>
975
976       •   MetaCPAN
977
978           <https://metacpan.org/release/List-MoreUtils>
979
980       •   CPAN Search
981
982           <http://search.cpan.org/dist/List-MoreUtils/>
983
984       •   Git Repository
985
986           <https://github.com/perl5-utils/List-MoreUtils>
987
988   Where can I go for help?
989       If you have a bug report, a patch or a suggestion, please open a new
990       report ticket at CPAN (but please check previous reports first in case
991       your issue has already been addressed) or open an issue on GitHub.
992
993       Report tickets should contain a detailed description of the bug or
994       enhancement request and at least an easily verifiable way of
995       reproducing the issue or fix. Patches are always welcome, too - and
996       it's cheap to send pull-requests on GitHub. Please keep in mind that
997       code changes are more likely accepted when they're bundled with an
998       approving test.
999
1000       If you think you've found a bug then please read "How to Report Bugs
1001       Effectively" by Simon Tatham:
1002       <http://www.chiark.greenend.org.uk/~sgtatham/bugs.html>.
1003
1004   Where can I go for help with a concrete version?
1005       Bugs and feature requests are accepted against the latest version only.
1006       To get patches for earlier versions, you need to get an agreement with
1007       a developer of your choice - who may or not report the issue and a
1008       suggested fix upstream (depends on the license you have chosen).
1009
1010   Business support and maintenance
1011       Generally, in volunteered projects, there is no right for support.
1012       While every maintainer is happy to improve the provided software, spare
1013       time is limited.
1014
1015       For those who have a use case which requires guaranteed support, one of
1016       the maintainers should be hired or contracted.  For business support
1017       you can contact Jens via his CPAN email address rehsackATcpan.org.
1018       Please keep in mind that business support is neither available for free
1019       nor are you eligible to receive any support based on the license
1020       distributed with this package.
1021

THANKS

1023   Tassilo von Parseval
1024       Credits go to a number of people: Steve Purkis for giving me namespace
1025       advice and James Keenan and Terrence Branno for their effort of keeping
1026       the CPAN tidier by making List::Utils obsolete.
1027
1028       Brian McCauley suggested the inclusion of apply() and provided the
1029       pure-Perl implementation for it.
1030
1031       Eric J. Roode asked me to add all functions from his module
1032       "List::MoreUtil" into this one. With minor modifications, the pure-Perl
1033       implementations of those are by him.
1034
1035       The bunch of people who almost immediately pointed out the many
1036       problems with the glitchy 0.07 release (Slaven Rezic, Ron Savage, CPAN
1037       testers).
1038
1039       A particularly nasty memory leak was spotted by Thomas A. Lowery.
1040
1041       Lars Thegler made me aware of problems with older Perl versions.
1042
1043       Anno Siegel de-orphaned each_arrayref().
1044
1045       David Filmer made me aware of a problem in each_arrayref that could
1046       ultimately lead to a segfault.
1047
1048       Ricardo Signes suggested the inclusion of part() and provided the Perl-
1049       implementation.
1050
1051       Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-
1052       implementation of part() work.
1053
1054   Jens Rehsack
1055       Credits goes to all people contributing feedback during the v0.400
1056       development releases.
1057
1058       Special thanks goes to David Golden who spent a lot of effort to
1059       develop a design to support current state of CPAN as well as ancient
1060       software somewhere in the dark. He also contributed a lot of patches to
1061       refactor the API frontend to welcome any user of List::MoreUtils - from
1062       ancient past to recently last used.
1063
1064       Toby Inkster provided a lot of useful feedback for sane importer code
1065       and was a nice sounding board for API discussions.
1066
1067       Peter Rabbitson provided a sane git repository setup containing entire
1068       package history.
1069

TODO

1071       A pile of requests from other people is still pending further
1072       processing in my mailbox. This includes:
1073
1074       •   delete_index
1075
1076       •   random_item
1077
1078       •   random_item_delete_index
1079
1080       •   list_diff_hash
1081
1082       •   list_diff_inboth
1083
1084       •   list_diff_infirst
1085
1086       •   list_diff_insecond
1087
1088           These were all suggested by Dan Muey.
1089
1090       •   listify
1091
1092           Always return a flat list when either a simple scalar value was
1093           passed or an array-reference. Suggested by Mark Summersault.
1094

SEE ALSO

1096       List::Util, List::AllUtils, List::UtilsBy
1097

AUTHOR

1099       Jens Rehsack <rehsack AT cpan.org>
1100
1101       Adam Kennedy <adamk@cpan.org>
1102
1103       Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>
1104
1106       Some parts copyright 2011 Aaron Crane.
1107
1108       Copyright 2004 - 2010 by Tassilo von Parseval
1109
1110       Copyright 2013 - 2017 by Jens Rehsack
1111
1112       All code added with 0.417 or later is licensed under the Apache
1113       License, Version 2.0 (the "License"); you may not use this file except
1114       in compliance with the License. You may obtain a copy of the License at
1115
1116        http://www.apache.org/licenses/LICENSE-2.0
1117
1118       Unless required by applicable law or agreed to in writing, software
1119       distributed under the License is distributed on an "AS IS" BASIS,
1120       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
1121       implied.  See the License for the specific language governing
1122       permissions and limitations under the License.
1123
1124       All code until 0.416 is licensed under the same terms as Perl itself,
1125       either Perl version 5.8.4 or, at your option, any later version of Perl
1126       5 you may have available.
1127
1128
1129
1130perl v5.32.1                      2021-01-27                List::MoreUtils(3)
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