| List::MoreUtils - Provide the stuff missing in List::Util |
List::MoreUtils - Provide the stuff missing in List::Util
# 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';
List::MoreUtils provides some trivial but commonly needed functionality on lists which is not going to go into the List::Util manpage.
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.
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.
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.
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).
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.
There are two schools of thought for how to evaluate a junction on an empty list:
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.
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.
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.
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.
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.
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.
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 }
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
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
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
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.
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 '', 'S1', A5' and complains about "Use of uninitialized value" my @s = distinct '', undef, 'S1', 'A5' # returns undef, 'S1', A5' and complains about "Use of uninitialized value" my @w = uniq undef, '', 'S1', 'A5'
distinct is an alias for uniq.
RT#49800 can be used to give feedback about this behavior.
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
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
Same as after but also includes the element for which BLOCK is true.
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.
Same as before but also includes the element for which BLOCK is true.
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]
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.
Like each_array, but the arguments are references to arrays, not the plain arrays.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
Similar to sort_by but compares its key values numerically.
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;
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;
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.
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.
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.
While contributions are appreciated, a contribution should not cause more effort for the maintainer than the contribution itself saves (see Open Source Contribution Etiquette).
To get more familiar where help could be needed - see the List::MoreUtils::Contributing manpage.
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 the List::Util manpage'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).
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:
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.
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).
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.
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 the List::Utils manpage 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.
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.
A pile of requests from other people is still pending further processing in my mailbox. This includes:
use the one module.
uniq_by(&@)
the List::Util manpage, the List::AllUtils manpage, the List::UtilsBy manpage
Jens Rehsack <rehsack AT cpan.org>
Adam Kennedy <adamk@cpan.org>
Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>
Some parts copyright 2011 Aaron Crane.
Copyright 2004 - 2010 by Tassilo von Parseval
Copyright 2013 - 2015 by Jens Rehsack
This library is free software; you can redistribute it and/or modify it 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.
| List::MoreUtils - Provide the stuff missing in List::Util |