1List::MoreUtils(3) User Contributed Perl Documentation List::MoreUtils(3)
2
6 List::MoreUtils - Provide the stuff missing in List::Util
7
9 # import specific functions
10 use List::MoreUtils qw(any uniq);
12 if ( any { /foo/ } uniq @has_duplicates ) {
14 # do stuff
15 }
16 # import everything
18 use List::MoreUtils ':all';
20 # import by API
22 # 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 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 use List::MoreUtils ':all';
47 use List::MoreUtils qw{ any firstidx };
49 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 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 use List::MoreUtils ':like_0.22';
59 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 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 use List::MoreUtils ':like_0.24';
69 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 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 use List::MoreUtils ':like_0.33';
83 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 There are two schools of thought for how to evaluate a junction on an
92 empty list:
93 · Reduction to an identity (boolean)
95 · Result is undefined (three-valued)
97 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 "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 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 Junctions with a "_u" suffix implement three-valued logic. Those
112 without are boolean.
113 all BLOCK LIST
115 all_u BLOCK LIST
117 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 print "All values are non-negative"
122 if all { $_ >= 0 } ($x, $y, $z);
123 For an empty LIST, "all" returns true (i.e. no values failed the
125 condition) and "all_u" returns "undef".
126 Thus, "all_u(@list)" is equivalent to "@list ? all(@list) : undef".
128 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 any BLOCK LIST
134 any_u BLOCK LIST
136 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 print "At least one non-negative value"
141 if any { $_ >= 0 } ($x, $y, $z);
142 For an empty LIST, "any" returns false and "any_u" returns "undef".
144 Thus, "any_u(@list)" is equivalent to "@list ? any(@list) : undef".
146 none BLOCK LIST
148 none_u BLOCK LIST
150 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 print "No non-negative values"
156 if none { $_ >= 0 } ($x, $y, $z);
157 For an empty LIST, "none" returns true (i.e. no values failed the
159 condition) and "none_u" returns "undef".
160 Thus, "none_u(@list)" is equivalent to "@list ? none(@list) : undef".
162 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 notall BLOCK LIST
168 notall_u BLOCK LIST
170 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 print "Not all values are non-negative"
176 if notall { $_ >= 0 } ($x, $y, $z);
177 For an empty LIST, "notall" returns false and "notall_u" returns
179 "undef".
180 Thus, "notall_u(@list)" is equivalent to "@list ? notall(@list) :
182 undef".
183 one BLOCK LIST
185 one_u BLOCK LIST
187 Returns a true value if precisely one item in LIST meets the criterion
189 given through BLOCK. Sets $_ for each item in LIST in turn:
190 print "Precisely one value defined"
192 if one { defined($_) } @list;
193 Returns false otherwise.
195 For an empty LIST, "one" returns false and "one_u" returns "undef".
197 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 Transformation
203 apply BLOCK LIST
204 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 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 Think of it as syntactic sugar for
219 for (my @mult = @list) { $_ *= 2 }
221 insert_after BLOCK VALUE LIST
223 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 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 insert_after_string STRING VALUE LIST
234 Inserts VALUE after the first item in LIST which is equal to STRING.
236 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 pairwise BLOCK ARRAY1 ARRAY2
244 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 @a = (1 .. 5);
251 @b = (11 .. 15);
252 @x = pairwise { $a + $b } @a, @b; # returns 12, 14, 16, 18, 20
253 # mesh with pairwise
255 @a = qw/a b c/;
256 @b = qw/1 2 3/;
257 @x = pairwise { ($a, $b) } @a, @b; # returns a, 1, b, 2, c, 3
258 mesh ARRAY1 ARRAY2 [ ARRAY3 ... ]
260 zip ARRAY1 ARRAY2 [ ARRAY3 ... ]
262 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 Examples:
267 @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 @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 "zip" is an alias for "mesh".
278 zip6
280 zip_unflatten
282 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 @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 @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 "zip_unflatten" is an alias for "zip6".
297 listcmp ARRAY0 ARRAY1 [ ARRAY2 ... ]
299 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 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 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 arrayify LIST[,LIST[,LIST...]]
316 Returns a list costisting of each element of given arrays. Recursive
318 arrays are flattened, too.
319 @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 uniq LIST
324 distinct LIST
326 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 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 "distinct" is an alias for "uniq".
342 RT#49800 can be used to give feedback about this behavior.
344 singleton LIST
346 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 my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5
354 duplicates LIST
356 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 my @y = duplicates 1,1,2,4,7,2,3,4,6,9; #returns 1,2,4
364 frequency LIST
366 Returns an associative list of distinct values and the corresponding
368 frequency.
369 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 occurrences LIST
376 Returns a new list of frequencies and the corresponding values from
378 LIST.
379 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 mode LIST
384 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 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 Partitioning
393 after BLOCK LIST
394 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 @x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9
400 after_incl BLOCK LIST
402 Same as "after" but also includes the element for which BLOCK is true.
404 before BLOCK LIST
406 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 before_incl BLOCK LIST
412 Same as "before" but also includes the element for which BLOCK is true.
414 part BLOCK LIST
416 Partitions LIST based on the return value of BLOCK which denotes into
418 which partition the current value is put.
419 Returns a list of the partitions thusly created. Each partition created
421 is a reference to an array.
422 my $i = 0;
424 my @part = part { $i++ % 2 } 1 .. 8; # returns [1, 3, 5, 7], [2, 4, 6, 8]
425 You can have a sparse list of partitions as well where non-set
427 partitions will be undef:
428 my @part = part { 2 } 1 .. 10; # returns undef, undef, [ 1 .. 10 ]
430 Be careful with negative values, though:
432 my @part = part { -1 } 1 .. 10;
434 __END__
435 Modification of non-creatable array value attempted, subscript -1 ...
436 Negative values are only ok when they refer to a partition previously
438 created:
439 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 samples COUNT LIST
445 Returns a new list containing COUNT random samples from LIST. Is
447 similar to "shuffle" in List::Util, but stops after COUNT.
448 @r = samples 10, 1..10; # same as shuffle
450 @r2 = samples 5, 1..10; # gives 5 values from 1..10;
451 Iteration
453 each_array ARRAY1 ARRAY2 ...
454 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 This is useful for looping over more than one array at once:
462 my $ea = each_array(@a, @b, @c);
464 while ( my ($a, $b, $c) = $ea->() ) { .... }
465 The iterator returns the empty list when it reached the end of all
467 arrays.
468 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 each_arrayref LIST
473 Like each_array, but the arguments are references to arrays, not the
475 plain arrays.
476 natatime EXPR, LIST
478 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 Example:
484 my @x = ('a' .. 'g');
486 my $it = natatime 3, @x;
487 while (my @vals = $it->())
488 {
489 print "@vals\n";
490 }
491 This prints
493 a b c
495 d e f
496 g
497 Searching
499 firstval BLOCK LIST
500 first_value BLOCK LIST
502 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 "first_value" is an alias for "firstval".
508 onlyval BLOCK LIST
510 only_value BLOCK LIST
512 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 "only_value" is an alias for "onlyval".
518 lastval BLOCK LIST
520 last_value BLOCK LIST
522 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 "last_value" is an alias for "lastval".
528 firstres BLOCK LIST
530 first_result BLOCK LIST
532 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 "first_result" is an alias for "firstres".
538 onlyres BLOCK LIST
540 only_result BLOCK LIST
542 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 "only_result" is an alias for "onlyres".
548 lastres BLOCK LIST
550 last_result BLOCK LIST
552 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 "last_result" is an alias for "lastres".
558 indexes BLOCK LIST
560 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 @x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9
567 firstidx BLOCK LIST
569 first_index BLOCK LIST
571 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 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 Returns "-1" if no such item could be found.
581 "first_index" is an alias for "firstidx".
583 onlyidx BLOCK LIST
585 only_index BLOCK LIST
587 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 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 Returns "-1" if either no such item or more than one of these has been
597 found.
598 "only_index" is an alias for "onlyidx".
600 lastidx BLOCK LIST
602 last_index BLOCK LIST
604 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 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 Returns "-1" if no such item could be found.
614 "last_index" is an alias for "lastidx".
616 Sorting
618 sort_by BLOCK LIST
619 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 sort_by { $_->name } @people
625 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 sort { $a->name cmp $b->name } @people
632 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 sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
638 This sorts strings by generating sort keys which zero-pad the embedded
640 numbers to some level (9 digits in this case), helping to ensure the
641 lexical sort puts them in the correct order.
642 nsort_by BLOCK LIST
644 Similar to sort_by but compares its key values numerically.
646 qsort BLOCK ARRAY
648 This sorts the given array in place using the given compare code.
650 Except for tiny compare code like "$a <=> $b", qsort is much faster
651 than Perl's "sort" depending on the version.
652 Compared 5.8 and 5.26:
654 my @rl;
656 for(my $i = 0; $i < 1E6; ++$i) { push @rl, rand(1E5) }
657 my $idx;
658 sub ext_cmp { $_[0] <=> $_[1] }
660 cmpthese( -60, {
662 'qsort' => sub {
663 my @qrl = @rl;
664 qsort { ext_cmp($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 5.8 results
685 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 5.26 results
693 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 Use it where external data sources might have to be compared (think of
701 Unix::Statgrab "tables").
702 "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 Searching in sorted Lists
709 bsearch BLOCK LIST
710 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 Returns a boolean value in scalar context. In list context, it returns
717 the element if it was found, otherwise the empty list.
718 bsearchidx BLOCK LIST
720 bsearch_index BLOCK LIST
722 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 Returns the index of found element, otherwise "-1".
729 "bsearch_index" is an alias for "bsearchidx".
731 lower_bound BLOCK LIST
733 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 @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 lower_bound has a complexity of O(log n).
743 upper_bound BLOCK LIST
745 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 @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 upper_bound has a complexity of O(log n).
755 equal_range BLOCK LIST
757 Returns a pair of indices containing the lower_bound and the
759 upper_bound.
760 Operations on sorted Lists
762 binsert BLOCK ITEM LIST
763 bsearch_insert BLOCK ITEM LIST
765 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 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 @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 You take care that the inserted element matches the compare result.
780 bremove BLOCK LIST
782 bsearch_remove BLOCK LIST
784 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 The item at the found position is removed and returned.
791 @l = (2,3,4,5,7);
793 bremove { $_ <=> 4 }, @l; # @l = (2,3,5,7);
794 Counting and calculation
796 true BLOCK LIST
797 Counts the number of elements in LIST for which the criterion in BLOCK
799 is true. Sets $_ for each item in LIST in turn:
800 printf "%i item(s) are defined", true { defined($_) } @list;
802 false BLOCK LIST
804 Counts the number of elements in LIST for which the criterion in BLOCK
806 is false. Sets $_ for each item in LIST in turn:
807 printf "%i item(s) are not defined", false { defined($_) } @list;
809 reduce_0 BLOCK LIST
811 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 The idea behind reduce_0 is summation (addition of a sequence of
818 numbers).
819 reduce_1 BLOCK LIST
821 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 The idea behind reduce_1 is product of a sequence of numbers.
828 reduce_u BLOCK LIST
830 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 This function has been added if one might need the extra of the index
837 value but need an individual initialization.
838 Use with caution: In most cases "reduce" in List::Util will do the job
840 better.
841 minmax LIST
843 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 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 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 minmaxstr LIST
859 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 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 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 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 my @x = apply { s/foo/bar/ } qw{ foo bar baz };
900 It has to be written as either
902 my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz';
904 or
906 my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/;
908 Perl 5.5.x and Perl 5.8.x don't suffer from this limitation.
910 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 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 You can find documentation for this module with the perldoc command.
924 perldoc List::MoreUtils
926 You can also look for information at:
928 · RT: CPAN's request tracker
930 <https://rt.cpan.org/Dist/Display.html?Name=List-MoreUtils>
932 · AnnoCPAN: Annotated CPAN documentation
934 <http://annocpan.org/dist/List-MoreUtils>
936 · CPAN Ratings
938 <http://cpanratings.perl.org/dist/List-MoreUtils>
940 · MetaCPAN
942 <https://metacpan.org/release/List-MoreUtils>
944 · CPAN Search
946 <http://search.cpan.org/dist/List-MoreUtils/>
948 · Git Repository
950 <https://github.com/perl5-utils/List-MoreUtils>
952 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 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 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 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 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 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 Brian McCauley suggested the inclusion of apply() and provided the
994 pure-Perl implementation for it.
995 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 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 A particularly nasty memory leak was spotted by Thomas A. Lowery.
1005 Lars Thegler made me aware of problems with older Perl versions.
1007 Anno Siegel de-orphaned each_arrayref().
1009 David Filmer made me aware of a problem in each_arrayref that could
1011 ultimately lead to a segfault.
1012 Ricardo Signes suggested the inclusion of part() and provided the Perl-
1014 implementation.
1015 Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-
1017 implementation of part() work.
1018 Jens Rehsack
1020 Credits goes to all people contributing feedback during the v0.400
1021 development releases.
1022 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 Toby Inkster provided a lot of useful feedback for sane importer code
1030 and was a nice sounding board for API discussions.
1031 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 · delete_index
1040 · random_item
1042 · random_item_delete_index
1044 · list_diff_hash
1046 · list_diff_inboth
1048 · list_diff_infirst
1050 · list_diff_insecond
1052 These were all suggested by Dan Muey.
1054 · listify
1056 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 Adam Kennedy <adamk@cpan.org>
1067 Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>
1069
1071 Some parts copyright 2011 Aaron Crane.
1072 Copyright 2004 - 2010 by Tassilo von Parseval
1074 Copyright 2013 - 2017 by Jens Rehsack
1076 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 http://www.apache.org/licenses/LICENSE-2.0
1082 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 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.
1092perl v5.30.1 2020-01-30 List::MoreUtils(3)