1List::SomeUtils(3) User Contributed Perl Documentation List::SomeUtils(3)
2
6 List::SomeUtils - Provide the stuff missing in List::Util
7
9 version 0.56
10
12 # import specific functions
13 use List::SomeUtils qw( any uniq );
14 if ( any {/foo/} uniq @has_duplicates ) {
16 # do stuff
18 }
19 # import everything
21 use List::SomeUtils ':all';
22
24 List::SomeUtils provides some trivial but commonly needed functionality
25 on lists which is not going to go into List::Util.
26 All of the below functions are implementable in only a couple of lines
28 of Perl code. Using the functions from this module however should give
29 slightly better performance as everything is implemented in C. The
30 pure-Perl implementation of these functions only serves as a fallback
31 in case the C portions of this module couldn't be compiled on this
32 machine.
33
35 You might wonder why this module exists when we already have
36 List::MoreUtils. In fact, this module is (nearly) the same code as is
37 found in LMU with no significant changes. However, the LMU distribution
38 depends on several modules for configuration (to run the Makefile.PL)
39 that some folks in the Perl community don't think are appropriate for a
40 module high upstream in the CPAN river.
41 I (Dave Rolsky) don't have a strong opinion on this, but I do like the
43 functions provided by LMU, and I'm tired of getting patches and PRs to
44 remove LMU from my code.
45 This distribution exists to let me use the functionality I like without
47 having to get into tiring arguments about issues I don't really care
48 about.
49
51 Default behavior
52 Nothing by default. To import all of this module's symbols use the
53 ":all" tag. Otherwise functions can be imported by name as usual:
54 use List::SomeUtils ':all';
56 use List::SomeUtils qw{ any firstidx };
58 Because historical changes to the API might make upgrading
60 List::SomeUtils difficult for some projects, the legacy API is
61 available via special import tags.
62
64 Junctions
65 Treatment of an empty list
66 There are two schools of thought for how to evaluate a junction on an
68 empty list:
69 · Reduction to an identity (boolean)
71 · Result is undefined (three-valued)
73 In the first case, the result of the junction applied to the empty list
75 is determined by a mathematical reduction to an identity depending on
76 whether the underlying comparison is "or" or "and". Conceptually:
77 "any are true" "all are true"
79 -------------- --------------
80 2 elements: A || B || 0 A && B && 1
81 1 element: A || 0 A && 1
82 0 elements: 0 1
83 In the second case, three-value logic is desired, in which a junction
85 applied to an empty list returns "undef" rather than true or false
86 Junctions with a "_u" suffix implement three-valued logic. Those
88 without are boolean.
89 all BLOCK LIST
91 all_u BLOCK LIST
93 Returns a true value if all items in LIST meet the criterion given
95 through BLOCK. Sets $_ for each item in LIST in turn:
96 print "All values are non-negative"
98 if all { $_ >= 0 } ($x, $y, $z);
99 For an empty LIST, "all" returns true (i.e. no values failed the
101 condition) and "all_u" returns "undef".
102 Thus, "all_u(@list)" is equivalent to "@list ? all(@list) : undef".
104 Note: because Perl treats "undef" as false, you must check the return
106 value of "all_u" with "defined" or you will get the opposite result of
107 what you expect.
108 any BLOCK LIST
110 any_u BLOCK LIST
112 Returns a true value if any item in LIST meets the criterion given
114 through BLOCK. Sets $_ for each item in LIST in turn:
115 print "At least one non-negative value"
117 if any { $_ >= 0 } ($x, $y, $z);
118 For an empty LIST, "any" returns false and "any_u" returns "undef".
120 Thus, "any_u(@list)" is equivalent to "@list ? any(@list) : undef".
122 none BLOCK LIST
124 none_u BLOCK LIST
126 Logically the negation of "any". Returns a true value if no item in
128 LIST meets the criterion given through BLOCK. Sets $_ for each item in
129 LIST in turn:
130 print "No non-negative values"
132 if none { $_ >= 0 } ($x, $y, $z);
133 For an empty LIST, "none" returns true (i.e. no values failed the
135 condition) and "none_u" returns "undef".
136 Thus, "none_u(@list)" is equivalent to "@list ? none(@list) : undef".
138 Note: because Perl treats "undef" as false, you must check the return
140 value of "none_u" with "defined" or you will get the opposite result of
141 what you expect.
142 notall BLOCK LIST
144 notall_u BLOCK LIST
146 Logically the negation of "all". Returns a true value if not all items
148 in LIST meet the criterion given through BLOCK. Sets $_ for each item
149 in LIST in turn:
150 print "Not all values are non-negative"
152 if notall { $_ >= 0 } ($x, $y, $z);
153 For an empty LIST, "notall" returns false and "notall_u" returns
155 "undef".
156 Thus, "notall_u(@list)" is equivalent to "@list ? notall(@list) :
158 undef".
159 one BLOCK LIST
161 one_u BLOCK LIST
163 Returns a true value if precisely one item in LIST meets the criterion
165 given through BLOCK. Sets $_ for each item in LIST in turn:
166 print "Precisely one value defined"
168 if one { defined($_) } @list;
169 Returns false otherwise.
171 For an empty LIST, "one" returns false and "one_u" returns "undef".
173 The expression "one BLOCK LIST" is almost equivalent to "1 == true
175 BLOCK LIST", except for short-cutting. Evaluation of BLOCK will
176 immediately stop at the second true value.
177 Transformation
179 apply BLOCK LIST
180 Applies BLOCK to each item in LIST and returns a list of the values
182 after BLOCK has been applied. In scalar context, the last element is
183 returned. This function is similar to "map" but will not modify the
184 elements of the input list:
185 my @list = (1 .. 4);
187 my @mult = apply { $_ *= 2 } @list;
188 print "\@list = @list\n";
189 print "\@mult = @mult\n";
190 __END__
191 @list = 1 2 3 4
192 @mult = 2 4 6 8
193 Think of it as syntactic sugar for
195 for (my @mult = @list) { $_ *= 2 }
197 insert_after BLOCK VALUE LIST
199 Inserts VALUE after the first item in LIST for which the criterion in
201 BLOCK is true. Sets $_ for each item in LIST in turn.
202 my @list = qw/This is a list/;
204 insert_after { $_ eq "a" } "longer" => @list;
205 print "@list";
206 __END__
207 This is a longer list
208 insert_after_string STRING VALUE LIST
210 Inserts VALUE after the first item in LIST which is equal to STRING.
212 my @list = qw/This is a list/;
214 insert_after_string "a", "longer" => @list;
215 print "@list";
216 __END__
217 This is a longer list
218 pairwise BLOCK ARRAY1 ARRAY2
220 Evaluates BLOCK for each pair of elements in ARRAY1 and ARRAY2 and
222 returns a new list consisting of BLOCK's return values. The two
223 elements are set to $a and $b. Note that those two are aliases to the
224 original value so changing them will modify the input arrays.
225 @a = (1 .. 5);
227 @b = (11 .. 15);
228 @x = pairwise { $a + $b } @a, @b; # returns 12, 14, 16, 18, 20
229 # mesh with pairwise
231 @a = qw/a b c/;
232 @b = qw/1 2 3/;
233 @x = pairwise { ($a, $b) } @a, @b; # returns a, 1, b, 2, c, 3
234 mesh ARRAY1 ARRAY2 [ ARRAY3 ... ]
236 zip ARRAY1 ARRAY2 [ ARRAY3 ... ]
238 Returns a list consisting of the first elements of each array, then the
240 second, then the third, etc, until all arrays are exhausted.
241 Examples:
243 @x = qw/a b c d/;
245 @y = qw/1 2 3 4/;
246 @z = mesh @x, @y; # returns a, 1, b, 2, c, 3, d, 4
247 @a = ('x');
249 @b = ('1', '2');
250 @c = qw/zip zap zot/;
251 @d = mesh @a, @b, @c; # x, 1, zip, undef, 2, zap, undef, undef, zot
252 "zip" is an alias for "mesh".
254 uniq LIST
256 distinct LIST
258 Returns a new list by stripping duplicate values in LIST by comparing
260 the values as hash keys, except that undef is considered separate from
261 ''. The order of elements in the returned list is the same as in LIST.
262 In scalar context, returns the number of unique elements in LIST.
263 my @x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 1 2 3 5 4
265 my $x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 5
266 # returns "Mike", "Michael", "Richard", "Rick"
267 my @n = distinct "Mike", "Michael", "Richard", "Rick", "Michael", "Rick"
268 # returns '', undef, 'S1', A5'
269 my @s = distinct '', undef, 'S1', 'A5'
270 # returns '', undef, 'S1', A5'
271 my @w = uniq undef, '', 'S1', 'A5'
272 "distinct" is an alias for "uniq".
274 RT#49800 can be used to give feedback about this behavior.
276 singleton
278 Returns a new list by stripping values in LIST occurring more than once
280 by comparing the values as hash keys, except that undef is considered
281 separate from ''. The order of elements in the returned list is the
282 same as in LIST. In scalar context, returns the number of elements
283 occurring only once in LIST.
284 my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5
286 Partitioning
288 after BLOCK LIST
289 Returns a list of the values of LIST after (and not including) the
291 point where BLOCK returns a true value. Sets $_ for each element in
292 LIST in turn.
293 @x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9
295 after_incl BLOCK LIST
297 Same as "after" but also includes the element for which BLOCK is true.
299 before BLOCK LIST
301 Returns a list of values of LIST up to (and not including) the point
303 where BLOCK returns a true value. Sets $_ for each element in LIST in
304 turn.
305 before_incl BLOCK LIST
307 Same as "before" but also includes the element for which BLOCK is true.
309 part BLOCK LIST
311 Partitions LIST based on the return value of BLOCK which denotes into
313 which partition the current value is put.
314 Returns a list of the partitions thusly created. Each partition created
316 is a reference to an array.
317 my $i = 0;
319 my @part = part { $i++ % 2 } 1 .. 8; # returns [1, 3, 5, 7], [2, 4, 6, 8]
320 You can have a sparse list of partitions as well where non-set
322 partitions will be undef:
323 my @part = part { 2 } 1 .. 10; # returns undef, undef, [ 1 .. 10 ]
325 Be careful with negative values, though:
327 my @part = part { -1 } 1 .. 10;
329 __END__
330 Modification of non-creatable array value attempted, subscript -1 ...
331 Negative values are only ok when they refer to a partition previously
333 created:
334 my @idx = ( 0, 1, -1 );
336 my $i = 0;
337 my @part = part { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
338 Iteration
340 each_array ARRAY1 ARRAY2 ...
341 Creates an array iterator to return the elements of the list of arrays
343 ARRAY1, ARRAY2 throughout ARRAYn in turn. That is, the first time it
344 is called, it returns the first element of each array. The next time,
345 it returns the second elements. And so on, until all elements are
346 exhausted.
347 This is useful for looping over more than one array at once:
349 my $ea = each_array(@a, @b, @c);
351 while ( my ($a, $b, $c) = $ea->() ) { .... }
352 The iterator returns the empty list when it reached the end of all
354 arrays.
355 If the iterator is passed an argument of '"index"', then it returns the
357 index of the last fetched set of values, as a scalar.
358 each_arrayref LIST
360 Like each_array, but the arguments are references to arrays, not the
362 plain arrays.
363 natatime EXPR, LIST
365 Creates an array iterator, for looping over an array in chunks of $n
367 items at a time. (n at a time, get it?). An example is probably a
368 better explanation than I could give in words.
369 Example:
371 my @x = ('a' .. 'g');
373 my $it = natatime 3, @x;
374 while (my @vals = $it->())
375 {
376 print "@vals\n";
377 }
378 This prints
380 a b c
382 d e f
383 g
384 Searching
386 bsearch BLOCK LIST
387 Performs a binary search on LIST which must be a sorted list of values.
389 BLOCK must return a negative value if the current element (stored in
390 $_) is smaller, a positive value if it is bigger and zero if it
391 matches.
392 Returns a boolean value in scalar context. In list context, it returns
394 the element if it was found, otherwise the empty list.
395 bsearchidx BLOCK LIST
397 bsearch_index BLOCK LIST
399 Performs a binary search on LIST which must be a sorted list of values.
401 BLOCK must return a negative value if the current element (stored in
402 $_) is smaller, a positive value if it is bigger and zero if it
403 matches.
404 Returns the index of found element, otherwise "-1".
406 "bsearch_index" is an alias for "bsearchidx".
408 firstval BLOCK LIST
410 first_value BLOCK LIST
412 Returns the first element in LIST for which BLOCK evaluates to true.
414 Each element of LIST is set to $_ in turn. Returns "undef" if no such
415 element has been found.
416 "first_value" is an alias for "firstval".
418 onlyval BLOCK LIST
420 only_value BLOCK LIST
422 Returns the only element in LIST for which BLOCK evaluates to true.
424 Sets $_ for each item in LIST in turn. Returns "undef" if no such
425 element has been found.
426 "only_value" is an alias for "onlyval".
428 lastval BLOCK LIST
430 last_value BLOCK LIST
432 Returns the last value in LIST for which BLOCK evaluates to true. Each
434 element of LIST is set to $_ in turn. Returns "undef" if no such
435 element has been found.
436 "last_value" is an alias for "lastval".
438 firstres BLOCK LIST
440 first_result BLOCK LIST
442 Returns the result of BLOCK for the first element in LIST for which
444 BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
445 Returns "undef" if no such element has been found.
446 "first_result" is an alias for "firstres".
448 onlyres BLOCK LIST
450 only_result BLOCK LIST
452 Returns the result of BLOCK for the first element in LIST for which
454 BLOCK evaluates to true. Sets $_ for each item in LIST in turn. Returns
455 "undef" if no such element has been found.
456 "only_result" is an alias for "onlyres".
458 lastres BLOCK LIST
460 last_result BLOCK LIST
462 Returns the result of BLOCK for the last element in LIST for which
464 BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
465 Returns "undef" if no such element has been found.
466 "last_result" is an alias for "lastres".
468 indexes BLOCK LIST
470 Evaluates BLOCK for each element in LIST (assigned to $_) and returns a
472 list of the indices of those elements for which BLOCK returned a true
473 value. This is just like "grep" only that it returns indices instead of
474 values:
475 @x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9
477 firstidx BLOCK LIST
479 first_index BLOCK LIST
481 Returns the index of the first element in LIST for which the criterion
483 in BLOCK is true. Sets $_ for each item in LIST in turn:
484 my @list = (1, 4, 3, 2, 4, 6);
486 printf "item with index %i in list is 4", firstidx { $_ == 4 } @list;
487 __END__
488 item with index 1 in list is 4
489 Returns "-1" if no such item could be found.
491 "first_index" is an alias for "firstidx".
493 onlyidx BLOCK LIST
495 only_index BLOCK LIST
497 Returns the index of the only element in LIST for which the criterion
499 in BLOCK is true. Sets $_ for each item in LIST in turn:
500 my @list = (1, 3, 4, 3, 2, 4);
502 printf "uniqe index of item 2 in list is %i", onlyidx { $_ == 2 } @list;
503 __END__
504 unique index of item 2 in list is 4
505 Returns "-1" if either no such item or more than one of these has been
507 found.
508 "only_index" is an alias for "onlyidx".
510 lastidx BLOCK LIST
512 last_index BLOCK LIST
514 Returns the index of the last element in LIST for which the criterion
516 in BLOCK is true. Sets $_ for each item in LIST in turn:
517 my @list = (1, 4, 3, 2, 4, 6);
519 printf "item with index %i in list is 4", lastidx { $_ == 4 } @list;
520 __END__
521 item with index 4 in list is 4
522 Returns "-1" if no such item could be found.
524 "last_index" is an alias for "lastidx".
526 Sorting
528 sort_by BLOCK LIST
529 Returns the list of values sorted according to the string values
531 returned by the KEYFUNC block or function. A typical use of this may be
532 to sort objects according to the string value of some accessor, such as
533 sort_by { $_->name } @people
535 The key function is called in scalar context, being passed each value
537 in turn as both $_ and the only argument in the parameters, @_. The
538 values are then sorted according to string comparisons on the values
539 returned. This is equivalent to
540 sort { $a->name cmp $b->name } @people
542 except that it guarantees the name accessor will be executed only once
544 per value. One interesting use-case is to sort strings which may have
545 numbers embedded in them "naturally", rather than lexically.
546 sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
548 This sorts strings by generating sort keys which zero-pad the embedded
550 numbers to some level (9 digits in this case), helping to ensure the
551 lexical sort puts them in the correct order.
552 nsort_by BLOCK LIST
554 Similar to sort_by but compares its key values numerically.
556 Counting and calculation
558 true BLOCK LIST
559 Counts the number of elements in LIST for which the criterion in BLOCK
561 is true. Sets $_ for each item in LIST in turn:
562 printf "%i item(s) are defined", true { defined($_) } @list;
564 false BLOCK LIST
566 Counts the number of elements in LIST for which the criterion in BLOCK
568 is false. Sets $_ for each item in LIST in turn:
569 printf "%i item(s) are not defined", false { defined($_) } @list;
571 minmax LIST
573 Calculates the minimum and maximum of LIST and returns a two element
575 list with the first element being the minimum and the second the
576 maximum. Returns the empty list if LIST was empty.
577 The "minmax" algorithm differs from a naive iteration over the list
579 where each element is compared to two values being the so far
580 calculated min and max value in that it only requires 3n/2 - 2
581 comparisons. Thus it is the most efficient possible algorithm.
582 However, the Perl implementation of it has some overhead simply due to
584 the fact that there are more lines of Perl code involved. Therefore,
585 LIST needs to be fairly big in order for "minmax" to win over a naive
586 implementation. This limitation does not apply to the XS version.
587 mode LIST
589 Calculates the most common items in the list and returns them as a
591 list. This is effectively done by string comparisons, so references
592 will be stringified. If they implement string overloading, this will be
593 used.
594 If more than one item appears the same number of times in the list, all
596 such items will be returned. For example, the mode of a unique list is
597 the list itself.
598 This function always returns a list. That means that in scalar context
600 you get a count indicating the number of modes in the list.
601
603 The maintenance goal is to preserve the documented semantics of the
604 API; bug fixes that bring actual behavior in line with semantics are
605 allowed. New API functions may be added over time. If a backwards
606 incompatible change is unavoidable, we will attempt to provide support
607 for the legacy API using the same export tag mechanism currently in
608 place.
609 This module attempts to use few non-core dependencies. Non-core
611 configuration and testing modules will be bundled when reasonable; run-
612 time dependencies will be added only if they deliver substantial
613 benefit.
614
616 There is a problem with a bug in 5.6.x perls. It is a syntax error to
617 write things like:
618 my @x = apply { s/foo/bar/ } qw{ foo bar baz };
620 It has to be written as either
622 my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz';
624 or
626 my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/;
628 Perl 5.5.x and Perl 5.8.x don't suffer from this limitation.
630 If you have a functionality that you could imagine being in this
632 module, please drop me a line. This module's policy will be less strict
633 than List::Util's when it comes to additions as it isn't a core module.
634 When you report bugs, it would be nice if you could additionally give
636 me the output of your program with the environment variable
637 "LIST_MOREUTILS_PP" set to a true value. That way I know where to look
638 for the problem (in XS, pure-Perl or possibly both).
639
641 Tassilo von Parseval
642 Credits go to a number of people: Steve Purkis for giving me namespace
643 advice and James Keenan and Terrence Branno for their effort of keeping
644 the CPAN tidier by making List::Util obsolete.
645 Brian McCauley suggested the inclusion of apply() and provided the
647 pure-Perl implementation for it.
648 Eric J. Roode asked me to add all functions from his module
650 "List::SomeUtil" into this one. With minor modifications, the pure-Perl
651 implementations of those are by him.
652 The bunch of people who almost immediately pointed out the many
654 problems with the glitchy 0.07 release (Slaven Rezic, Ron Savage, CPAN
655 testers).
656 A particularly nasty memory leak was spotted by Thomas A. Lowery.
658 Lars Thegler made me aware of problems with older Perl versions.
660 Anno Siegel de-orphaned each_arrayref().
662 David Filmer made me aware of a problem in each_arrayref that could
664 ultimately lead to a segfault.
665 Ricardo Signes suggested the inclusion of part() and provided the Perl-
667 implementation.
668 Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-
670 implementation of part() work.
671 Jens Rehsack
673 Credits goes to all people contributing feedback during the v0.400
674 development releases.
675 Special thanks goes to David Golden who spent a lot of effort to
677 develop a design to support current state of CPAN as well as ancient
678 software somewhere in the dark. He also contributed a lot of patches to
679 refactor the API frontend to welcome any user of List::SomeUtils - from
680 ancient past to recently last used.
681 Toby Inkster provided a lot of useful feedback for sane importer code
683 and was a nice sounding board for API discussions.
684 Peter Rabbitson provided a sane git repository setup containing entire
686 package history.
687
689 A pile of requests from other people is still pending further
690 processing in my mailbox. This includes:
691 · List::Util export pass-through
693 Allow List::SomeUtils to pass-through the regular List::Util
695 functions to end users only need to "use" the one module.
696 · uniq_by(&@)
698 Use code-reference to extract a key based on which the uniqueness
700 is determined. Suggested by Aaron Crane.
701 · delete_index
703 · random_item
705 · random_item_delete_index
707 · list_diff_hash
709 · list_diff_inboth
711 · list_diff_infirst
713 · list_diff_insecond
715 These were all suggested by Dan Muey.
717 · listify
719 Always return a flat list when either a simple scalar value was
721 passed or an array-reference. Suggested by Mark Summersault.
722
724 List::Util, List::AllUtils, List::UtilsBy
725
727 Some parts copyright 2011 Aaron Crane.
728 Copyright 2004 - 2010 by Tassilo von Parseval
730 Copyright 2013 - 2015 by Jens Rehsack
732
734 Bugs may be submitted at
735 <https://github.com/houseabsolute/List-SomeUtils/issues>.
736 I am also usually active on IRC as 'autarch' on "irc://irc.perl.org".
738
740 The source code repository for List-SomeUtils can be found at
741 <https://github.com/houseabsolute/List-SomeUtils>.
742
744 If you'd like to thank me for the work I've done on this module, please
745 consider making a "donation" to me via PayPal. I spend a lot of free
746 time creating free software, and would appreciate any support you'd
747 care to offer.
748 Please note that I am not suggesting that you must do this in order for
750 me to continue working on this particular software. I will continue to
751 do so, inasmuch as I have in the past, for as long as it interests me.
752 Similarly, a donation made in this way will probably not make me work
754 on this software much more, unless I get so many donations that I can
755 consider working on free software full time (let's all have a chuckle
756 at that together).
757 To donate, log into PayPal and send money to autarch@urth.org, or use
759 the button at <http://www.urth.org/~autarch/fs-donation.html>.
760
762 · Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>
763 · Adam Kennedy <adamk@cpan.org>
765 · Jens Rehsack <rehsack@cpan.org>
767 · Dave Rolsky <autarch@urth.org>
769
771 · Aaron Crane <arc@cpan.org>
772 · BackPan <BackPan>
774 · Brad Forschinger <bnjf@bnjf.id.au>
776 · David Golden <dagolden@cpan.org>
778 · jddurand <jeandamiendurand@free.fr>
780 · Jens Rehsack <sno@netbsd.org>
782 · J.R. Mash <jrmash@cpan.org>
784 · Karen Etheridge <ether@cpan.org>
786 · Ricardo Signes <rjbs@cpan.org>
788 · Toby Inkster <mail@tobyinkster.co.uk>
790 · Tokuhiro Matsuno <tokuhirom@cpan.org>
792 · Tom Wyant <wyant@cpan.org>
794
796 This software is copyright (c) 2017 by Dave Rolsky <autarch@urth.org>.
797 This is free software; you can redistribute it and/or modify it under
799 the same terms as the Perl 5 programming language system itself.
800 The full text of the license can be found in the LICENSE file included
802 with this distribution.
803perl v5.28.0 2017-07-22 List::SomeUtils(3)