1List::MoreUtils(3) User Contributed Perl Documentation List::MoreUtils(3)
2
3
4
6 List::MoreUtils - Provide the stuff missing in List::Util
7
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
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
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
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. Allowes 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 costisting 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 occuring less than twice
358 by comparing the values as hash keys, except that undef is considered
359 separate from ''. The order of elements in the returned list is the
360 same as in LIST. In scalar context, returns the number of elements
361 occurring only 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 occuring 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 Partitioning
393 after BLOCK LIST
394
395 Returns a list of the values of LIST after (and not including) the
396 point where BLOCK returns a true value. Sets $_ for each element in
397 LIST in turn.
398
399 @x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9
400
401 after_incl BLOCK LIST
402
403 Same as "after" but also includes the element for which BLOCK is true.
404
405 before BLOCK LIST
406
407 Returns a list of values of LIST up to (and not including) the point
408 where BLOCK returns a true value. Sets $_ for each element in LIST in
409 turn.
410
411 before_incl BLOCK LIST
412
413 Same as "before" but also includes the element for which BLOCK is true.
414
415 part BLOCK LIST
416
417 Partitions LIST based on the return value of BLOCK which denotes into
418 which partition the current value is put.
419
420 Returns a list of the partitions thusly created. Each partition created
421 is a reference to an array.
422
423 my $i = 0;
424 my @part = part { $i++ % 2 } 1 .. 8; # returns [1, 3, 5, 7], [2, 4, 6, 8]
425
426 You can have a sparse list of partitions as well where non-set
427 partitions will be undef:
428
429 my @part = part { 2 } 1 .. 10; # returns undef, undef, [ 1 .. 10 ]
430
431 Be careful with negative values, though:
432
433 my @part = part { -1 } 1 .. 10;
434 __END__
435 Modification of non-creatable array value attempted, subscript -1 ...
436
437 Negative values are only ok when they refer to a partition previously
438 created:
439
440 my @idx = ( 0, 1, -1 );
441 my $i = 0;
442 my @part = part { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
443
444 samples COUNT LIST
445
446 Returns a new list containing COUNT random samples from LIST. Is
447 similar to "shuffle" in List::Util, but stops after COUNT.
448
449 @r = samples 10, 1..10; # same as shuffle
450 @r2 = samples 5, 1..10; # gives 5 values from 1..10;
451
452 Iteration
453 each_array ARRAY1 ARRAY2 ...
454
455 Creates an array iterator to return the elements of the list of arrays
456 ARRAY1, ARRAY2 throughout ARRAYn in turn. That is, the first time it
457 is called, it returns the first element of each array. The next time,
458 it returns the second elements. And so on, until all elements are
459 exhausted.
460
461 This is useful for looping over more than one array at once:
462
463 my $ea = each_array(@a, @b, @c);
464 while ( my ($a, $b, $c) = $ea->() ) { .... }
465
466 The iterator returns the empty list when it reached the end of all
467 arrays.
468
469 If the iterator is passed an argument of '"index"', then it returns the
470 index of the last fetched set of values, as a scalar.
471
472 each_arrayref LIST
473
474 Like each_array, but the arguments are references to arrays, not the
475 plain arrays.
476
477 natatime EXPR, LIST
478
479 Creates an array iterator, for looping over an array in chunks of $n
480 items at a time. (n at a time, get it?). An example is probably a
481 better explanation than I could give in words.
482
483 Example:
484
485 my @x = ('a' .. 'g');
486 my $it = natatime 3, @x;
487 while (my @vals = $it->())
488 {
489 print "@vals\n";
490 }
491
492 This prints
493
494 a b c
495 d e f
496 g
497
498 Searching
499 firstval BLOCK LIST
500
501 first_value BLOCK LIST
502
503 Returns the first element in LIST for which BLOCK evaluates to true.
504 Each element of LIST is set to $_ in turn. Returns "undef" if no such
505 element has been found.
506
507 "first_value" is an alias for "firstval".
508
509 onlyval BLOCK LIST
510
511 only_value BLOCK LIST
512
513 Returns the only element in LIST for which BLOCK evaluates to true.
514 Sets $_ for each item in LIST in turn. Returns "undef" if no such
515 element has been found.
516
517 "only_value" is an alias for "onlyval".
518
519 lastval BLOCK LIST
520
521 last_value BLOCK LIST
522
523 Returns the last value in LIST for which BLOCK evaluates to true. Each
524 element of LIST is set to $_ in turn. Returns "undef" if no such
525 element has been found.
526
527 "last_value" is an alias for "lastval".
528
529 firstres BLOCK LIST
530
531 first_result BLOCK LIST
532
533 Returns the result of BLOCK for the first element in LIST for which
534 BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
535 Returns "undef" if no such element has been found.
536
537 "first_result" is an alias for "firstres".
538
539 onlyres BLOCK LIST
540
541 only_result BLOCK LIST
542
543 Returns the result of BLOCK for the first element in LIST for which
544 BLOCK evaluates to true. Sets $_ for each item in LIST in turn. Returns
545 "undef" if no such element has been found.
546
547 "only_result" is an alias for "onlyres".
548
549 lastres BLOCK LIST
550
551 last_result BLOCK LIST
552
553 Returns the result of BLOCK for the last element in LIST for which
554 BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
555 Returns "undef" if no such element has been found.
556
557 "last_result" is an alias for "lastres".
558
559 indexes BLOCK LIST
560
561 Evaluates BLOCK for each element in LIST (assigned to $_) and returns a
562 list of the indices of those elements for which BLOCK returned a true
563 value. This is just like "grep" only that it returns indices instead of
564 values:
565
566 @x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9
567
568 firstidx BLOCK LIST
569
570 first_index BLOCK LIST
571
572 Returns the index of the first element in LIST for which the criterion
573 in BLOCK is true. Sets $_ for each item in LIST in turn:
574
575 my @list = (1, 4, 3, 2, 4, 6);
576 printf "item with index %i in list is 4", firstidx { $_ == 4 } @list;
577 __END__
578 item with index 1 in list is 4
579
580 Returns "-1" if no such item could be found.
581
582 "first_index" is an alias for "firstidx".
583
584 onlyidx BLOCK LIST
585
586 only_index BLOCK LIST
587
588 Returns the index of the only element in LIST for which the criterion
589 in BLOCK is true. Sets $_ for each item in LIST in turn:
590
591 my @list = (1, 3, 4, 3, 2, 4);
592 printf "uniqe index of item 2 in list is %i", onlyidx { $_ == 2 } @list;
593 __END__
594 unique index of item 2 in list is 4
595
596 Returns "-1" if either no such item or more than one of these has been
597 found.
598
599 "only_index" is an alias for "onlyidx".
600
601 lastidx BLOCK LIST
602
603 last_index BLOCK LIST
604
605 Returns the index of the last element in LIST for which the criterion
606 in BLOCK is true. Sets $_ for each item in LIST in turn:
607
608 my @list = (1, 4, 3, 2, 4, 6);
609 printf "item with index %i in list is 4", lastidx { $_ == 4 } @list;
610 __END__
611 item with index 4 in list is 4
612
613 Returns "-1" if no such item could be found.
614
615 "last_index" is an alias for "lastidx".
616
617 Sorting
618 sort_by BLOCK LIST
619
620 Returns the list of values sorted according to the string values
621 returned by the KEYFUNC block or function. A typical use of this may be
622 to sort objects according to the string value of some accessor, such as
623
624 sort_by { $_->name } @people
625
626 The key function is called in scalar context, being passed each value
627 in turn as both $_ and the only argument in the parameters, @_. The
628 values are then sorted according to string comparisons on the values
629 returned. This is equivalent to
630
631 sort { $a->name cmp $b->name } @people
632
633 except that it guarantees the name accessor will be executed only once
634 per value. One interesting use-case is to sort strings which may have
635 numbers embedded in them "naturally", rather than lexically.
636
637 sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
638
639 This sorts strings by generating sort keys which zero-pad the embedded
640 numbers to some level (9 digits in this case), helping to ensure the
641 lexical sort puts them in the correct order.
642
643 nsort_by BLOCK LIST
644
645 Similar to sort_by but compares its key values numerically.
646
647 qsort BLOCK ARRAY
648
649 This sorts the given array in place using the given compare code.
650 Except for tiny compare code like "$a <=> $b", qsort is much faster
651 than Perl's "sort" depending on the version.
652
653 Compared 5.8 and 5.26:
654
655 my @rl;
656 for(my $i = 0; $i < 1E6; ++$i) { push @rl, rand(1E5) }
657 my $idx;
658
659 sub ext_cmp { $_[0] <=> $_[1] }
660
661 cmpthese( -60, {
662 'qsort' => sub {
663 my @qrl = @rl;
664 qsort { ext_cmp($a, $b) } @qrl;
665 $idx = bsearchidx { ext_cmp($_, $rl[0]) } @qrl
666 },
667 'reverse qsort' => sub {
668 my @qrl = @rl;
669 qsort { ext_cmp($b, $a) } @qrl;
670 $idx = bsearchidx { ext_cmp($rl[0], $_) } @qrl
671 },
672 'sort' => sub {
673 my @srl = @rl;
674 @srl = sort { ext_cmp($a, $b) } @srl;
675 $idx = bsearchidx { ext_cmp($_, $rl[0]) } @srl
676 },
677 'reverse sort' => sub {
678 my @srl = @rl;
679 @srl = sort { ext_cmp($b, $a) } @srl;
680 $idx = bsearchidx { ext_cmp($rl[0], $_) } @srl
681 },
682 });
683
684 5.8 results
685
686 s/iter reverse sort sort reverse qsort qsort
687 reverse sort 6.21 -- -0% -8% -10%
688 sort 6.19 0% -- -7% -10%
689 reverse qsort 5.73 8% 8% -- -2%
690 qsort 5.60 11% 11% 2% --
691
692 5.26 results
693
694 s/iter reverse sort sort reverse qsort qsort
695 reverse sort 4.54 -- -0% -96% -96%
696 sort 4.52 0% -- -96% -96%
697 reverse qsort 0.203 2139% 2131% -- -19%
698 qsort 0.164 2666% 2656% 24% --
699
700 Use it where external data sources might have to be compared (think of
701 Unix::Statgrab "tables").
702
703 "qsort" is available from List::MoreUtils::XS only. It's insane to
704 maintain a wrapper around Perl's sort nor having a pure Perl
705 implementation. One could create a flip-book in same speed as PP runs a
706 qsort.
707
708 Searching in sorted Lists
709 bsearch BLOCK LIST
710
711 Performs a binary search on LIST which must be a sorted list of values.
712 BLOCK must return a negative value if the current element (stored in
713 $_) is smaller, a positive value if it is bigger and zero if it
714 matches.
715
716 Returns a boolean value in scalar context. In list context, it returns
717 the element if it was found, otherwise the empty list.
718
719 bsearchidx BLOCK LIST
720
721 bsearch_index BLOCK LIST
722
723 Performs a binary search on LIST which must be a sorted list of values.
724 BLOCK must return a negative value if the current element (stored in
725 $_) is smaller, a positive value if it is bigger and zero if it
726 matches.
727
728 Returns the index of found element, otherwise "-1".
729
730 "bsearch_index" is an alias for "bsearchidx".
731
732 lower_bound BLOCK LIST
733
734 Returns the index of the first element in LIST which does not compare
735 less than val. Technically it's the first element in LIST which does
736 not return a value below zero when passed to BLOCK.
737
738 @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);
739 $lb = lower_bound { $_ <=> 2 } @ids; # returns 2
740 $lb = lower_bound { $_ <=> 4 } @ids; # returns 10
741
742 lower_bound has a complexity of O(log n).
743
744 upper_bound BLOCK LIST
745
746 Returns the index of the first element in LIST which does not compare
747 greater than val. Technically it's the first element in LIST which does
748 not return a value below or equal to zero when passed to BLOCK.
749
750 @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);
751 $lb = upper_bound { $_ <=> 2 } @ids; # returns 4
752 $lb = upper_bound { $_ <=> 4 } @ids; # returns 14
753
754 upper_bound has a complexity of O(log n).
755
756 equal_range BLOCK LIST
757
758 Returns a pair of indices containing the lower_bound and the
759 upper_bound.
760
761 Operations on sorted Lists
762 binsert BLOCK ITEM LIST
763
764 bsearch_insert BLOCK ITEM LIST
765
766 Performs a binary search on LIST which must be a sorted list of values.
767 BLOCK must return a negative value if the current element (stored in
768 $_) is smaller, a positive value if it is bigger and zero if it
769 matches.
770
771 ITEM is inserted at the index where the ITEM should be placed (based on
772 above search). That means, it's inserted before the next bigger
773 element.
774
775 @l = (2,3,5,7);
776 binsert { $_ <=> 4 } 4, @l; # @l = (2,3,4,5,7)
777 binsert { $_ <=> 6 } 42, @l; # @l = (2,3,4,42,7)
778
779 You take care that the inserted element matches the compare result.
780
781 bremove BLOCK LIST
782
783 bsearch_remove BLOCK LIST
784
785 Performs a binary search on LIST which must be a sorted list of values.
786 BLOCK must return a negative value if the current element (stored in
787 $_) is smaller, a positive value if it is bigger and zero if it
788 matches.
789
790 The item at the found position is removed and returned.
791
792 @l = (2,3,4,5,7);
793 bremove { $_ <=> 4 }, @l; # @l = (2,3,5,7);
794
795 Counting and calculation
796 true BLOCK LIST
797
798 Counts the number of elements in LIST for which the criterion in BLOCK
799 is true. Sets $_ for each item in LIST in turn:
800
801 printf "%i item(s) are defined", true { defined($_) } @list;
802
803 false BLOCK LIST
804
805 Counts the number of elements in LIST for which the criterion in BLOCK
806 is false. Sets $_ for each item in LIST in turn:
807
808 printf "%i item(s) are not defined", false { defined($_) } @list;
809
810 reduce_0 BLOCK LIST
811
812 Reduce LIST by calling BLOCK in scalar context for each element of
813 LIST. $a contains the progressional result and is initialized with 0.
814 $b contains the current processed element of LIST and $_ contains the
815 index of the element in $b.
816
817 The idea behind reduce_0 is summation (addition of a sequence of
818 numbers).
819
820 reduce_1 BLOCK LIST
821
822 Reduce LIST by calling BLOCK in scalar context for each element of
823 LIST. $a contains the progressional result and is initialized with 1.
824 $b contains the current processed element of LIST and $_ contains the
825 index of the element in $b.
826
827 The idea behind reduce_1 is product of a sequence of numbers.
828
829 reduce_u BLOCK LIST
830
831 Reduce LIST by calling BLOCK in scalar context for each element of
832 LIST. $a contains the progressional result and is initialized with 1.
833 $b contains the current processed element of LIST and $_ contains the
834 index of the element in $b.
835
836 This function has been added if one might need the extra of the index
837 value but need an individual initialization.
838
839 Use with caution: In most cases "reduce" in List::Util will do the job
840 better.
841
842 minmax LIST
843
844 Calculates the minimum and maximum of LIST and returns a two element
845 list with the first element being the minimum and the second the
846 maximum. Returns the empty list if LIST was empty.
847
848 The "minmax" algorithm differs from a naive iteration over the list
849 where each element is compared to two values being the so far
850 calculated min and max value in that it only requires 3n/2 - 2
851 comparisons. Thus it is the most efficient possible algorithm.
852
853 However, the Perl implementation of it has some overhead simply due to
854 the fact that there are more lines of Perl code involved. Therefore,
855 LIST needs to be fairly big in order for "minmax" to win over a naive
856 implementation. This limitation does not apply to the XS version.
857
858 minmaxstr LIST
859
860 Computes the minimum and maximum of LIST using string compare and
861 returns a two element list with the first element being the minimum and
862 the second the maximum. Returns the empty list if LIST was empty.
863
864 The implementation is similar to "minmax".
865
867 When "LIST_MOREUTILS_PP" is set, the module will always use the pure-
868 Perl implementation and not the XS one. This environment variable is
869 really just there for the test-suite to force testing the Perl
870 implementation, and possibly for reporting of bugs. I don't see any
871 reason to use it in a production environment.
872
874 The maintenance goal is to preserve the documented semantics of the
875 API; bug fixes that bring actual behavior in line with semantics are
876 allowed. New API functions may be added over time. If a backwards
877 incompatible change is unavoidable, we will attempt to provide support
878 for the legacy API using the same export tag mechanism currently in
879 place.
880
881 This module attempts to use few non-core dependencies. Non-core
882 configuration and testing modules will be bundled when reasonable; run-
883 time dependencies will be added only if they deliver substantial
884 benefit.
885
887 While contributions are appreciated, a contribution should not cause
888 more effort for the maintainer than the contribution itself saves (see
889 Open Source Contribution Etiquette
890 <http://tirania.org/blog/archive/2010/Dec-31.html>).
891
892 To get more familiar where help could be needed - see
893 List::MoreUtils::Contributing.
894
896 There is a problem with a bug in 5.6.x perls. It is a syntax error to
897 write things like:
898
899 my @x = apply { s/foo/bar/ } qw{ foo bar baz };
900
901 It has to be written as either
902
903 my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz';
904
905 or
906
907 my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/;
908
909 Perl 5.5.x and Perl 5.8.x don't suffer from this limitation.
910
911 If you have a functionality that you could imagine being in this
912 module, please drop me a line. This module's policy will be less strict
913 than List::Util's when it comes to additions as it isn't a core module.
914
915 When you report bugs, it would be nice if you could additionally give
916 me the output of your program with the environment variable
917 "LIST_MOREUTILS_PP" set to a true value. That way I know where to look
918 for the problem (in XS, pure-Perl or possibly both).
919
921 Bugs should always be submitted via the CPAN bug tracker.
922
923 You can find documentation for this module with the perldoc command.
924
925 perldoc List::MoreUtils
926
927 You can also look for information at:
928
929 · RT: CPAN's request tracker
930
931 <https://rt.cpan.org/Dist/Display.html?Name=List-MoreUtils>
932
933 · AnnoCPAN: Annotated CPAN documentation
934
935 <http://annocpan.org/dist/List-MoreUtils>
936
937 · CPAN Ratings
938
939 <http://cpanratings.perl.org/dist/List-MoreUtils>
940
941 · MetaCPAN
942
943 <https://metacpan.org/release/List-MoreUtils>
944
945 · CPAN Search
946
947 <http://search.cpan.org/dist/List-MoreUtils/>
948
949 · Git Repository
950
951 <https://github.com/perl5-utils/List-MoreUtils>
952
953 Where can I go for help?
954 If you have a bug report, a patch or a suggestion, please open a new
955 report ticket at CPAN (but please check previous reports first in case
956 your issue has already been addressed) or open an issue on GitHub.
957
958 Report tickets should contain a detailed description of the bug or
959 enhancement request and at least an easily verifiable way of
960 reproducing the issue or fix. Patches are always welcome, too - and
961 it's cheap to send pull-requests on GitHub. Please keep in mind that
962 code changes are more likely accepted when they're bundled with an
963 approving test.
964
965 If you think you've found a bug then please read "How to Report Bugs
966 Effectively" by Simon Tatham:
967 <http://www.chiark.greenend.org.uk/~sgtatham/bugs.html>.
968
969 Where can I go for help with a concrete version?
970 Bugs and feature requests are accepted against the latest version only.
971 To get patches for earlier versions, you need to get an agreement with
972 a developer of your choice - who may or not report the issue and a
973 suggested fix upstream (depends on the license you have chosen).
974
975 Business support and maintenance
976 Generally, in volunteered projects, there is no right for support.
977 While every maintainer is happy to improve the provided software, spare
978 time is limited.
979
980 For those who have a use case which requires guaranteed support, one of
981 the maintainers should be hired or contracted. For business support
982 you can contact Jens via his CPAN email address rehsackATcpan.org.
983 Please keep in mind that business support is neither available for free
984 nor are you eligible to receive any support based on the license
985 distributed with this package.
986
988 Tassilo von Parseval
989 Credits go to a number of people: Steve Purkis for giving me namespace
990 advice and James Keenan and Terrence Branno for their effort of keeping
991 the CPAN tidier by making List::Utils obsolete.
992
993 Brian McCauley suggested the inclusion of apply() and provided the
994 pure-Perl implementation for it.
995
996 Eric J. Roode asked me to add all functions from his module
997 "List::MoreUtil" into this one. With minor modifications, the pure-Perl
998 implementations of those are by him.
999
1000 The bunch of people who almost immediately pointed out the many
1001 problems with the glitchy 0.07 release (Slaven Rezic, Ron Savage, CPAN
1002 testers).
1003
1004 A particularly nasty memory leak was spotted by Thomas A. Lowery.
1005
1006 Lars Thegler made me aware of problems with older Perl versions.
1007
1008 Anno Siegel de-orphaned each_arrayref().
1009
1010 David Filmer made me aware of a problem in each_arrayref that could
1011 ultimately lead to a segfault.
1012
1013 Ricardo Signes suggested the inclusion of part() and provided the Perl-
1014 implementation.
1015
1016 Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-
1017 implementation of part() work.
1018
1019 Jens Rehsack
1020 Credits goes to all people contributing feedback during the v0.400
1021 development releases.
1022
1023 Special thanks goes to David Golden who spent a lot of effort to
1024 develop a design to support current state of CPAN as well as ancient
1025 software somewhere in the dark. He also contributed a lot of patches to
1026 refactor the API frontend to welcome any user of List::MoreUtils - from
1027 ancient past to recently last used.
1028
1029 Toby Inkster provided a lot of useful feedback for sane importer code
1030 and was a nice sounding board for API discussions.
1031
1032 Peter Rabbitson provided a sane git repository setup containing entire
1033 package history.
1034
1036 A pile of requests from other people is still pending further
1037 processing in my mailbox. This includes:
1038
1039 · delete_index
1040
1041 · random_item
1042
1043 · random_item_delete_index
1044
1045 · list_diff_hash
1046
1047 · list_diff_inboth
1048
1049 · list_diff_infirst
1050
1051 · list_diff_insecond
1052
1053 These were all suggested by Dan Muey.
1054
1055 · listify
1056
1057 Always return a flat list when either a simple scalar value was
1058 passed or an array-reference. Suggested by Mark Summersault.
1059
1061 List::Util, List::AllUtils, List::UtilsBy
1062
1064 Jens Rehsack <rehsack AT cpan.org>
1065
1066 Adam Kennedy <adamk@cpan.org>
1067
1068 Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>
1069
1071 Some parts copyright 2011 Aaron Crane.
1072
1073 Copyright 2004 - 2010 by Tassilo von Parseval
1074
1075 Copyright 2013 - 2017 by Jens Rehsack
1076
1077 All code added with 0.417 or later is licensed under the Apache
1078 License, Version 2.0 (the "License"); you may not use this file except
1079 in compliance with the License. You may obtain a copy of the License at
1080
1081 http://www.apache.org/licenses/LICENSE-2.0
1082
1083 Unless required by applicable law or agreed to in writing, software
1084 distributed under the License is distributed on an "AS IS" BASIS,
1085 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
1086 implied. See the License for the specific language governing
1087 permissions and limitations under the License.
1088
1089 All code until 0.416 is licensed under the same terms as Perl itself,
1090 either Perl version 5.8.4 or, at your option, any later version of Perl
1091 5 you may have available.
1092
1093
1094
1095perl v5.30.1 2020-01-30 List::MoreUtils(3)