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# NAME List::MoreUtils - Provide the stuff missing in List::Util # SYNOPSIS # import specific functions use List::MoreUtils qw(any uniq); if ( any { /foo/ } uniq @has_duplicates ) { # do stuff } # import everything use List::MoreUtils ':all'; # import by API # has "original" any/all/none/notall behavior use List::MoreUtils ':like_0.22'; # 0.22 + bsearch use List::MoreUtils ':like_0.24'; # has "simplified" any/all/none/notall behavior + (n)sort_by use List::MoreUtils ':like_0.33'; # DESCRIPTION **List::MoreUtils** provides some trivial but commonly needed functionality on lists which is not going to go into [List::Util](https://metacpan.org/pod/List::Util). All of the below functions are implementable in only a couple of lines of Perl code. Using the functions from this module however should give slightly better performance as everything is implemented in C. The pure-Perl implementation of these functions only serves as a fallback in case the C portions of this module couldn't be compiled on this machine. # EXPORTS ## Default behavior Nothing by default. To import all of this module's symbols use the `:all` tag. Otherwise functions can be imported by name as usual: use List::MoreUtils ':all'; use List::MoreUtils qw{ any firstidx }; Because historical changes to the API might make upgrading List::MoreUtils difficult for some projects, the legacy API is available via special import tags. ## Like version 0.22 (last release with original API) This API was available from 2006 to 2009, returning undef for empty lists on `all`/`any`/`none`/`notall`: use List::MoreUtils ':like_0.22'; This import tag will import all functions available as of version 0.22. However, it will import `any_u` as `any`, `all_u` as `all`, `none_u` as `none`, and `notall_u` as `notall`. ## Like version 0.24 (first incompatible change) This API was available from 2010 to 2011. It changed the return value of `none` and added the `bsearch` function. use List::MoreUtils ':like_0.24'; This import tag will import all functions available as of version 0.24. However it will import `any_u` as `any`, `all_u` as `all`, and `notall_u` as `notall`. It will import `none` as described in the documentation below (true for empty list). ## Like version 0.33 (second incompatible change) This API was available from 2011 to 2014. It is widely used in several CPAN modules and thus it's closest to the current API. It changed the return values of `any`, `all`, and `notall`. It added the `sort_by` and `nsort_by` functions and the `distinct` alias for `uniq`. It omitted `bsearch`. use List::MoreUtils ':like_0.33'; This import tag will import all functions available as of version 0.33. Note: it will not import `bsearch` for consistency with the 0.33 API. # FUNCTIONS ## Junctions ### _Treatment of an empty list_ There are two schools of thought for how to evaluate a junction on an empty list: - Reduction to an identity (boolean) - Result is undefined (three-valued) In the first case, the result of the junction applied to the empty list is determined by a mathematical reduction to an identity depending on whether the underlying comparison is "or" or "and". Conceptually: "any are true" "all are true" -------------- -------------- 2 elements: A || B || 0 A && B && 1 1 element: A || 0 A && 1 0 elements: 0 1 In the second case, three-value logic is desired, in which a junction applied to an empty list returns `undef` rather than true or false Junctions with a `_u` suffix implement three-valued logic. Those without are boolean. ### all BLOCK LIST ### all\_u BLOCK LIST Returns a true value if all items in LIST meet the criterion given through BLOCK. Sets `$_` for each item in LIST in turn: print "All values are non-negative" if all { $_ >= 0 } ($x, $y, $z); For an empty LIST, `all` returns true (i.e. no values failed the condition) and `all_u` returns `undef`. Thus, `all_u(@list)` is equivalent to `@list ? all(@list) : undef`. **Note**: because Perl treats `undef` as false, you must check the return value of `all_u` with `defined` or you will get the opposite result of what you expect. ### any BLOCK LIST ### any\_u BLOCK LIST Returns a true value if any item in LIST meets the criterion given through BLOCK. Sets `$_` for each item in LIST in turn: print "At least one non-negative value" if any { $_ >= 0 } ($x, $y, $z); For an empty LIST, `any` returns false and `any_u` returns `undef`. Thus, `any_u(@list)` is equivalent to `@list ? any(@list) : undef`. ### none BLOCK LIST ### none\_u BLOCK LIST Logically the negation of `any`. Returns a true value if no item in LIST meets the criterion given through BLOCK. Sets `$_` for each item in LIST in turn: print "No non-negative values" if none { $_ >= 0 } ($x, $y, $z); For an empty LIST, `none` returns true (i.e. no values failed the condition) and `none_u` returns `undef`. Thus, `none_u(@list)` is equivalent to `@list ? none(@list) : undef`. **Note**: because Perl treats `undef` as false, you must check the return value of `none_u` with `defined` or you will get the opposite result of what you expect. ### notall BLOCK LIST ### notall\_u BLOCK LIST Logically the negation of `all`. Returns a true value if not all items in LIST meet the criterion given through BLOCK. Sets `$_` for each item in LIST in turn: print "Not all values are non-negative" if notall { $_ >= 0 } ($x, $y, $z); For an empty LIST, `notall` returns false and `notall_u` returns `undef`. Thus, `notall_u(@list)` is equivalent to `@list ? notall(@list) : undef`. ### one BLOCK LIST ### one\_u BLOCK LIST Returns a true value if precisely one item in LIST meets the criterion given through BLOCK. Sets `$_` for each item in LIST in turn: print "Precisely one value defined" if one { defined($_) } @list; Returns false otherwise. For an empty LIST, `one` returns false and `one_u` returns `undef`. The expression `one BLOCK LIST` is almost equivalent to `1 == true BLOCK LIST`, except for short-cutting. Evaluation of BLOCK will immediately stop at the second true value. ## Transformation ### apply BLOCK LIST Applies BLOCK to each item in LIST and returns a list of the values after BLOCK has been applied. In scalar context, the last element is returned. This function is similar to `map` but will not modify the elements of the input list: my @list = (1 .. 4); my @mult = apply { $_ *= 2 } @list; print "\@list = @list\n"; print "\@mult = @mult\n"; __END__ @list = 1 2 3 4 @mult = 2 4 6 8 Think of it as syntactic sugar for for (my @mult = @list) { $_ *= 2 } ### insert\_after BLOCK VALUE LIST Inserts VALUE after the first item in LIST for which the criterion in BLOCK is true. Sets `$_` for each item in LIST in turn. my @list = qw/This is a list/; insert_after { $_ eq "a" } "longer" => @list; print "@list"; __END__ This is a longer list ### insert\_after\_string STRING VALUE LIST Inserts VALUE after the first item in LIST which is equal to STRING. my @list = qw/This is a list/; insert_after_string "a", "longer" => @list; print "@list"; __END__ This is a longer list ### pairwise BLOCK ARRAY1 ARRAY2 Evaluates BLOCK for each pair of elements in ARRAY1 and ARRAY2 and returns a new list consisting of BLOCK's return values. The two elements are set to `$a` and `$b`. Note that those two are aliases to the original value so changing them will modify the input arrays. @a = (1 .. 5); @b = (11 .. 15); @x = pairwise { $a + $b } @a, @b; # returns 12, 14, 16, 18, 20 # mesh with pairwise @a = qw/a b c/; @b = qw/1 2 3/; @x = pairwise { ($a, $b) } @a, @b; # returns a, 1, b, 2, c, 3 ### mesh ARRAY1 ARRAY2 \[ ARRAY3 ... \] ### zip ARRAY1 ARRAY2 \[ ARRAY3 ... \] Returns a list consisting of the first elements of each array, then the second, then the third, etc, until all arrays are exhausted. Examples: @x = qw/a b c d/; @y = qw/1 2 3 4/; @z = mesh @x, @y; # returns a, 1, b, 2, c, 3, d, 4 @a = ('x'); @b = ('1', '2'); @c = qw/zip zap zot/; @d = mesh @a, @b, @c; # x, 1, zip, undef, 2, zap, undef, undef, zot `zip` is an alias for `mesh`. ### zip6 ### zip\_unflatten Returns a list of arrays consisting of the first elements of each array, then the second, then the third, etc, until all arrays are exhausted. @x = qw/a b c d/; @y = qw/1 2 3 4/; @z = zip6 @x, @y; # returns [a, 1], [b, 2], [c, 3], [d, 4] @a = ('x'); @b = ('1', '2'); @c = qw/zip zap zot/; @d = zip6 @a, @b, @c; # [x, 1, zip], [undef, 2, zap], [undef, undef, zot] `zip_unflatten` is an alias for `zip6`. ### listcmp ARRAY0 ARRAY1 \[ ARRAY2 ... \] Returns an associative list of elements and every _id_ of the list it was found in. Allowes easy implementation of @a & @b, @a | @b, @a ^ @b and so on. Undefined entries in any given array are skipped. my @a = qw(one two three four five six seven eight nine ten eleven twelve thirteen); my @b = qw(two three five seven eleven thirteen seventeen); my @c = qw(one one two three five eight thirteen twentyone); my %cmp = listcmp @a, @b, @c; # returns (one => [0, 2], two => [0, 1, 2], three => [0, 1, 2], four => [0], ...) my @seq = (1, 2, 3); my @prim = (undef, 2, 3, 5); my @fib = (1, 1, 2); my $cmp = listcmp @seq, @prim, @fib; # returns { 1 => [0, 2], 2 => [0, 1, 2], 3 => [0, 1], 5 => [1] } ### arrayify LIST\[,LIST\[,LIST...\]\] Returns a list costisting of each element of given arrays. Recursive arrays are flattened, too. @a = (1, [[2], 3], 4, [5], 6, [7], 8, 9); @l = arrayify @a; # returns 1, 2, 3, 4, 5, 6, 7, 8, 9 ### uniq LIST ### distinct LIST Returns a new list by stripping duplicate values in LIST by comparing the values as hash keys, except that undef is considered separate from ''. The order of elements in the returned list is the same as in LIST. In scalar context, returns the number of unique elements in LIST. my @x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 1 2 3 5 4 my $x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 5 # returns "Mike", "Michael", "Richard", "Rick" my @n = distinct "Mike", "Michael", "Richard", "Rick", "Michael", "Rick" # returns "A8", "", undef, "A5", "S1" my @s = distinct "A8", "", undef, "A5", "S1", "A5", "A8" # returns "Giulia", "Giulietta", undef, "", 156, "GTA", "GTV", 159, "Brera", "4C" my @w = uniq "Giulia", "Giulietta", undef, "", 156, "GTA", "GTV", 159, "Brera", "4C", "Giulietta", "Giulia" `distinct` is an alias for `uniq`. **RT#49800** can be used to give feedback about this behavior. ### singleton LIST Returns a new list by stripping values in LIST occurring more than once by comparing the values as hash keys, except that undef is considered separate from ''. The order of elements in the returned list is the same as in LIST. In scalar context, returns the number of elements occurring only once in LIST. my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5 ### duplicates LIST Returns a new list by stripping values in LIST occuring less than twice by comparing the values as hash keys, except that undef is considered separate from ''. The order of elements in the returned list is the same as in LIST. In scalar context, returns the number of elements occurring only once in LIST. my @y = duplicates 1,1,2,4,7,2,3,4,6,9; #returns 1,2,4 ### frequency LIST Returns an associative list of distinct values and the corresponding frequency. my @f = frequency values %radio_nrw; # returns ( # 'Deutschlandfunk (DLF)' => 9, 'WDR 3' => 10, # 'WDR 4' => 11, 'WDR 5' => 14, 'WDR Eins Live' => 14, # 'Deutschlandradio Kultur' => 8,...) ### occurrences LIST Returns a new list of frequencies and the corresponding values from LIST. my @o = occurrences ((1) x 3, (2) x 4, (3) x 2, (4) x 7, (5) x 2, (6) x 4); # @o = (undef, undef, [3, 5], [1], [2, 6], undef, undef, [4]); ### mode LIST Returns the modal value of LIST. In scalar context, just the modal value is returned, in list context all probes occuring _modal_ times are returned, too. 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); # @m = (7, 4, 8) - bimodal LIST ## Partitioning ### after BLOCK LIST Returns a list of the values of LIST after (and not including) the point where BLOCK returns a true value. Sets `$_` for each element in LIST in turn. @x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9 ### after\_incl BLOCK LIST Same as `after` but also includes the element for which BLOCK is true. ### before BLOCK LIST Returns a list of values of LIST up to (and not including) the point where BLOCK returns a true value. Sets `$_` for each element in LIST in turn. ### before\_incl BLOCK LIST Same as `before` but also includes the element for which BLOCK is true. ### part BLOCK LIST Partitions LIST based on the return value of BLOCK which denotes into which partition the current value is put. Returns a list of the partitions thusly created. Each partition created is a reference to an array. my $i = 0; my @part = part { $i++ % 2 } 1 .. 8; # returns [1, 3, 5, 7], [2, 4, 6, 8] You can have a sparse list of partitions as well where non-set partitions will be undef: my @part = part { 2 } 1 .. 10; # returns undef, undef, [ 1 .. 10 ] Be careful with negative values, though: my @part = part { -1 } 1 .. 10; __END__ Modification of non-creatable array value attempted, subscript -1 ... Negative values are only ok when they refer to a partition previously created: my @idx = ( 0, 1, -1 ); my $i = 0; my @part = part { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8] ### samples COUNT LIST Returns a new list containing COUNT random samples from LIST. Is similar to ["shuffle" in List::Util](https://metacpan.org/pod/List::Util#shuffle), but stops after COUNT. @r = samples 10, 1..10; # same as shuffle @r2 = samples 5, 1..10; # gives 5 values from 1..10; ## Iteration ### each\_array ARRAY1 ARRAY2 ... Creates an array iterator to return the elements of the list of arrays ARRAY1, ARRAY2 throughout ARRAYn in turn. That is, the first time it is called, it returns the first element of each array. The next time, it returns the second elements. And so on, until all elements are exhausted. This is useful for looping over more than one array at once: my $ea = each_array(@a, @b, @c); while ( my ($a, $b, $c) = $ea->() ) { .... } The iterator returns the empty list when it reached the end of all arrays. If the iterator is passed an argument of '`index`', then it returns the index of the last fetched set of values, as a scalar. ### each\_arrayref LIST Like each\_array, but the arguments are references to arrays, not the plain arrays. ### natatime EXPR, LIST Creates an array iterator, for looping over an array in chunks of `$n` items at a time. (n at a time, get it?). An example is probably a better explanation than I could give in words. Example: my @x = ('a' .. 'g'); my $it = natatime 3, @x; while (my @vals = $it->()) { print "@vals\n"; } This prints a b c d e f g ## Searching ### firstval BLOCK LIST ### first\_value BLOCK LIST Returns the first element in LIST for which BLOCK evaluates to true. Each element of LIST is set to `$_` in turn. Returns `undef` if no such element has been found. `first_value` is an alias for `firstval`. ### onlyval BLOCK LIST ### only\_value BLOCK LIST Returns the only element in LIST for which BLOCK evaluates to true. Sets `$_` for each item in LIST in turn. Returns `undef` if no such element has been found. `only_value` is an alias for `onlyval`. ### lastval BLOCK LIST ### last\_value BLOCK LIST Returns the last value in LIST for which BLOCK evaluates to true. Each element of LIST is set to `$_` in turn. Returns `undef` if no such element has been found. `last_value` is an alias for `lastval`. ### firstres BLOCK LIST ### first\_result BLOCK LIST Returns the result of BLOCK for the first element in LIST for which BLOCK evaluates to true. Each element of LIST is set to `$_` in turn. Returns `undef` if no such element has been found. `first_result` is an alias for `firstres`. ### onlyres BLOCK LIST ### only\_result BLOCK LIST Returns the result of BLOCK for the first element in LIST for which BLOCK evaluates to true. Sets `$_` for each item in LIST in turn. Returns `undef` if no such element has been found. `only_result` is an alias for `onlyres`. ### lastres BLOCK LIST ### last\_result BLOCK LIST Returns the result of BLOCK for the last element in LIST for which BLOCK evaluates to true. Each element of LIST is set to `$_` in turn. Returns `undef` if no such element has been found. `last_result` is an alias for `lastres`. ### indexes BLOCK LIST Evaluates BLOCK for each element in LIST (assigned to `$_`) and returns a list of the indices of those elements for which BLOCK returned a true value. This is just like `grep` only that it returns indices instead of values: @x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9 ### firstidx BLOCK LIST ### first\_index BLOCK LIST Returns the index of the first element in LIST for which the criterion in BLOCK is true. Sets `$_` for each item in LIST in turn: my @list = (1, 4, 3, 2, 4, 6); printf "item with index %i in list is 4", firstidx { $_ == 4 } @list; __END__ item with index 1 in list is 4 Returns `-1` if no such item could be found. `first_index` is an alias for `firstidx`. ### onlyidx BLOCK LIST ### only\_index BLOCK LIST Returns the index of the only element in LIST for which the criterion in BLOCK is true. Sets `$_` for each item in LIST in turn: my @list = (1, 3, 4, 3, 2, 4); printf "uniqe index of item 2 in list is %i", onlyidx { $_ == 2 } @list; __END__ unique index of item 2 in list is 4 Returns `-1` if either no such item or more than one of these has been found. `only_index` is an alias for `onlyidx`. ### lastidx BLOCK LIST ### last\_index BLOCK LIST Returns the index of the last element in LIST for which the criterion in BLOCK is true. Sets `$_` for each item in LIST in turn: my @list = (1, 4, 3, 2, 4, 6); printf "item with index %i in list is 4", lastidx { $_ == 4 } @list; __END__ item with index 4 in list is 4 Returns `-1` if no such item could be found. `last_index` is an alias for `lastidx`. ## Sorting ### sort\_by BLOCK LIST Returns the list of values sorted according to the string values returned by the KEYFUNC block or function. A typical use of this may be to sort objects according to the string value of some accessor, such as sort_by { $_->name } @people The key function is called in scalar context, being passed each value in turn as both $\_ and the only argument in the parameters, @\_. The values are then sorted according to string comparisons on the values returned. This is equivalent to sort { $a->name cmp $b->name } @people except that it guarantees the name accessor will be executed only once per value. One interesting use-case is to sort strings which may have numbers embedded in them "naturally", rather than lexically. sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings This sorts strings by generating sort keys which zero-pad the embedded numbers to some level (9 digits in this case), helping to ensure the lexical sort puts them in the correct order. ### nsort\_by BLOCK LIST Similar to sort\_by but compares its key values numerically. ### qsort BLOCK ARRAY This sorts the given array **in place** using the given compare code. Except for tiny compare code like `$a <=> $b`, qsort is much faster than Perl's `sort` depending on the version. Compared 5.8 and 5.26: my @rl; for(my $i = 0; $i < 1E6; ++$i) { push @rl, rand(1E5) } my $idx; sub ext_cmp { $_[0] <=> $_[1] } cmpthese( -60, { 'qsort' => sub { my @qrl = @rl; qsort { ext_cmp($a, $b) } @qrl; $idx = bsearchidx { ext_cmp($_, $rl[0]) } @qrl }, 'reverse qsort' => sub { my @qrl = @rl; qsort { ext_cmp($b, $a) } @qrl; $idx = bsearchidx { ext_cmp($rl[0], $_) } @qrl }, 'sort' => sub { my @srl = @rl; @srl = sort { ext_cmp($a, $b) } @srl; $idx = bsearchidx { ext_cmp($_, $rl[0]) } @srl }, 'reverse sort' => sub { my @srl = @rl; @srl = sort { ext_cmp($b, $a) } @srl; $idx = bsearchidx { ext_cmp($rl[0], $_) } @srl }, }); 5.8 results s/iter reverse sort sort reverse qsort qsort reverse sort 6.21 -- -0% -8% -10% sort 6.19 0% -- -7% -10% reverse qsort 5.73 8% 8% -- -2% qsort 5.60 11% 11% 2% -- 5.26 results s/iter reverse sort sort reverse qsort qsort reverse sort 4.54 -- -0% -96% -96% sort 4.52 0% -- -96% -96% reverse qsort 0.203 2139% 2131% -- -19% qsort 0.164 2666% 2656% 24% -- Use it where external data sources might have to be compared (think of [Unix::Statgrab](https://metacpan.org/pod/Unix::Statgrab) "tables"). `qsort` is available from List::MoreUtils::XS only. It's insane to maintain a wrapper around Perl's sort nor having a pure Perl implementation. One could create a flip-book in same speed as PP runs a qsort. ## Searching in sorted Lists ### bsearch BLOCK LIST Performs a binary search on LIST which must be a sorted list of values. BLOCK must return a negative value if the current element (stored in `$_`) is smaller, a positive value if it is bigger and zero if it matches. Returns a boolean value in scalar context. In list context, it returns the element if it was found, otherwise the empty list. ### bsearchidx BLOCK LIST ### bsearch\_index BLOCK LIST Performs a binary search on LIST which must be a sorted list of values. BLOCK must return a negative value if the current element (stored in `$_`) is smaller, a positive value if it is bigger and zero if it matches. Returns the index of found element, otherwise `-1`. `bsearch_index` is an alias for `bsearchidx`. ### lower\_bound BLOCK LIST Returns the index of the first element in LIST which does not compare _less than val_. Technically it's the first element in LIST which does not return a value below zero when passed to BLOCK. @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); $lb = lower_bound { $_ <=> 2 } @ids; # returns 2 $lb = lower_bound { $_ <=> 4 } @ids; # returns 10 lower\_bound has a complexity of O(log n). ### upper\_bound BLOCK LIST Returns the index of the first element in LIST which does not compare _greater than val_. Technically it's the first element in LIST which does not return a value below or equal to zero when passed to BLOCK. @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); $lb = upper_bound { $_ <=> 2 } @ids; # returns 4 $lb = upper_bound { $_ <=> 4 } @ids; # returns 14 upper\_bound has a complexity of O(log n). ### equal\_range BLOCK LIST Returns a pair of indices containing the lower\_bound and the upper\_bound. ## Operations on sorted Lists ### binsert BLOCK ITEM LIST ### bsearch\_insert BLOCK ITEM LIST Performs a binary search on LIST which must be a sorted list of values. BLOCK must return a negative value if the current element (stored in `$_`) is smaller, a positive value if it is bigger and zero if it matches. ITEM is inserted at the index where the ITEM should be placed (based on above search). That means, it's inserted before the next bigger element. @l = (2,3,5,7); binsert { $_ <=> 4 } 4, @l; # @l = (2,3,4,5,7) binsert { $_ <=> 6 } 42, @l; # @l = (2,3,4,42,7) You take care that the inserted element matches the compare result. ### bremove BLOCK LIST ### bsearch\_remove BLOCK LIST Performs a binary search on LIST which must be a sorted list of values. BLOCK must return a negative value if the current element (stored in `$_`) is smaller, a positive value if it is bigger and zero if it matches. The item at the found position is removed and returned. @l = (2,3,4,5,7); bremove { $_ <=> 4 }, @l; # @l = (2,3,5,7); ## Counting and calculation ### true BLOCK LIST Counts the number of elements in LIST for which the criterion in BLOCK is true. Sets `$_` for each item in LIST in turn: printf "%i item(s) are defined", true { defined($_) } @list; ### false BLOCK LIST Counts the number of elements in LIST for which the criterion in BLOCK is false. Sets `$_` for each item in LIST in turn: printf "%i item(s) are not defined", false { defined($_) } @list; ### reduce\_0 BLOCK LIST Reduce LIST by calling BLOCK in scalar context for each element of LIST. `$a` contains the progressional result and is initialized with 0. `$b` contains the current processed element of LIST and `$_` contains the index of the element in `$b`. The idea behind reduce\_0 is **summation** (addition of a sequence of numbers). ### reduce\_1 BLOCK LIST Reduce LIST by calling BLOCK in scalar context for each element of LIST. `$a` contains the progressional result and is initialized with 1. `$b` contains the current processed element of LIST and `$_` contains the index of the element in `$b`. The idea behind reduce\_1 is product of a sequence of numbers. ### reduce\_u BLOCK LIST Reduce LIST by calling BLOCK in scalar context for each element of LIST. `$a` contains the progressional result and is initialized with 1. `$b` contains the current processed element of LIST and `$_` contains the index of the element in `$b`. This function has been added if one might need the extra of the index value but need an individual initialization. **Use with caution**: In most cases ["reduce" in List::Util](https://metacpan.org/pod/List::Util#reduce) will do the job better. ### minmax LIST Calculates the minimum and maximum of LIST and returns a two element list with the first element being the minimum and the second the maximum. Returns the empty list if LIST was empty. The `minmax` algorithm differs from a naive iteration over the list where each element is compared to two values being the so far calculated min and max value in that it only requires 3n/2 - 2 comparisons. Thus it is the most efficient possible algorithm. However, the Perl implementation of it has some overhead simply due to the fact that there are more lines of Perl code involved. Therefore, LIST needs to be fairly big in order for `minmax` to win over a naive implementation. This limitation does not apply to the XS version. ### minmaxstr LIST Computes the minimum and maximum of LIST using string compare and returns a two element list with the first element being the minimum and the second the maximum. Returns the empty list if LIST was empty. The implementation is similar to `minmax`. # ENVIRONMENT When `LIST_MOREUTILS_PP` is set, the module will always use the pure-Perl implementation and not the XS one. This environment variable is really just there for the test-suite to force testing the Perl implementation, and possibly for reporting of bugs. I don't see any reason to use it in a production environment. # MAINTENANCE The maintenance goal is to preserve the documented semantics of the API; bug fixes that bring actual behavior in line with semantics are allowed. New API functions may be added over time. If a backwards incompatible change is unavoidable, we will attempt to provide support for the legacy API using the same export tag mechanism currently in place. This module attempts to use few non-core dependencies. Non-core configuration and testing modules will be bundled when reasonable; run-time dependencies will be added only if they deliver substantial benefit. # CONTRIBUTING While contributions are appreciated, a contribution should not cause more effort for the maintainer than the contribution itself saves (see [Open Source Contribution Etiquette](http://tirania.org/blog/archive/2010/Dec-31.html)). To get more familiar where help could be needed - see [List::MoreUtils::Contributing](https://metacpan.org/pod/List::MoreUtils::Contributing). # BUGS There is a problem with a bug in 5.6.x perls. It is a syntax error to write things like: my @x = apply { s/foo/bar/ } qw{ foo bar baz }; It has to be written as either my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz'; or my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/; Perl 5.5.x and Perl 5.8.x don't suffer from this limitation. If you have a functionality that you could imagine being in this module, please drop me a line. This module's policy will be less strict than [List::Util](https://metacpan.org/pod/List::Util)'s when it comes to additions as it isn't a core module. When you report bugs, it would be nice if you could additionally give me the output of your program with the environment variable `LIST_MOREUTILS_PP` set to a true value. That way I know where to look for the problem (in XS, pure-Perl or possibly both). # SUPPORT Bugs should always be submitted via the CPAN bug tracker. You can find documentation for this module with the perldoc command. perldoc List::MoreUtils You can also look for information at: - RT: CPAN's request tracker [https://rt.cpan.org/Dist/Display.html?Name=List-MoreUtils](https://rt.cpan.org/Dist/Display.html?Name=List-MoreUtils) - AnnoCPAN: Annotated CPAN documentation [http://annocpan.org/dist/List-MoreUtils](http://annocpan.org/dist/List-MoreUtils) - CPAN Ratings [http://cpanratings.perl.org/dist/List-MoreUtils](http://cpanratings.perl.org/dist/List-MoreUtils) - MetaCPAN [https://metacpan.org/release/List-MoreUtils](https://metacpan.org/release/List-MoreUtils) - CPAN Search [http://search.cpan.org/dist/List-MoreUtils/](http://search.cpan.org/dist/List-MoreUtils/) - Git Repository [https://github.com/perl5-utils/List-MoreUtils](https://github.com/perl5-utils/List-MoreUtils) ## Where can I go for help? If you have a bug report, a patch or a suggestion, please open a new report ticket at CPAN (but please check previous reports first in case your issue has already been addressed) or open an issue on GitHub. Report tickets should contain a detailed description of the bug or enhancement request and at least an easily verifiable way of reproducing the issue or fix. Patches are always welcome, too - and it's cheap to send pull-requests on GitHub. Please keep in mind that code changes are more likely accepted when they're bundled with an approving test. If you think you've found a bug then please read "How to Report Bugs Effectively" by Simon Tatham: [http://www.chiark.greenend.org.uk/~sgtatham/bugs.html](http://www.chiark.greenend.org.uk/~sgtatham/bugs.html). ## Where can I go for help with a concrete version? Bugs and feature requests are accepted against the latest version only. To get patches for earlier versions, you need to get an agreement with a developer of your choice - who may or not report the issue and a suggested fix upstream (depends on the license you have chosen). ## Business support and maintenance Generally, in volunteered projects, there is no right for support. While every maintainer is happy to improve the provided software, spare time is limited. For those who have a use case which requires guaranteed support, one of the maintainers should be hired or contracted. For business support you can contact Jens via his CPAN email address rehsackATcpan.org. Please keep in mind that business support is neither available for free nor are you eligible to receive any support based on the license distributed with this package. # THANKS ## Tassilo von Parseval Credits go to a number of people: Steve Purkis for giving me namespace advice and James Keenan and Terrence Branno for their effort of keeping the CPAN tidier by making [List::Utils](https://metacpan.org/pod/List::Utils) obsolete. Brian McCauley suggested the inclusion of apply() and provided the pure-Perl implementation for it. Eric J. Roode asked me to add all functions from his module `List::MoreUtil` into this one. With minor modifications, the pure-Perl implementations of those are by him. The bunch of people who almost immediately pointed out the many problems with the glitchy 0.07 release (Slaven Rezic, Ron Savage, CPAN testers). A particularly nasty memory leak was spotted by Thomas A. Lowery. Lars Thegler made me aware of problems with older Perl versions. Anno Siegel de-orphaned each\_arrayref(). David Filmer made me aware of a problem in each\_arrayref that could ultimately lead to a segfault. Ricardo Signes suggested the inclusion of part() and provided the Perl-implementation. Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-implementation of part() work. ## Jens Rehsack Credits goes to all people contributing feedback during the v0.400 development releases. Special thanks goes to David Golden who spent a lot of effort to develop a design to support current state of CPAN as well as ancient software somewhere in the dark. He also contributed a lot of patches to refactor the API frontend to welcome any user of List::MoreUtils - from ancient past to recently last used. Toby Inkster provided a lot of useful feedback for sane importer code and was a nice sounding board for API discussions. Peter Rabbitson provided a sane git repository setup containing entire package history. # TODO A pile of requests from other people is still pending further processing in my mailbox. This includes: - delete\_index - random\_item - random\_item\_delete\_index - list\_diff\_hash - list\_diff\_inboth - list\_diff\_infirst - list\_diff\_insecond These were all suggested by Dan Muey. - listify Always return a flat list when either a simple scalar value was passed or an array-reference. Suggested by Mark Summersault. # SEE ALSO [List::Util](https://metacpan.org/pod/List::Util), [List::AllUtils](https://metacpan.org/pod/List::AllUtils), [List::UtilsBy](https://metacpan.org/pod/List::UtilsBy) # AUTHOR Jens Rehsack <rehsack AT cpan.org> Adam Kennedy <adamk@cpan.org> Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de> # COPYRIGHT AND LICENSE Some parts copyright 2011 Aaron Crane. Copyright 2004 - 2010 by Tassilo von Parseval Copyright 2013 - 2017 by Jens Rehsack All code added with 0.417 or later is licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. All code until 0.416 is licensed under the same terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of Perl 5 you may have available.