NAME¶
List::MoreUtils - Provide the stuff missing in List::Util
SYNOPSIS¶
use List::MoreUtils qw{
any all none notall true false
firstidx first_index lastidx last_index
insert_after insert_after_string
apply indexes
after after_incl before before_incl
firstval first_value lastval last_value
each_array each_arrayref
pairwise natatime
mesh zip uniq distinct minmax part
};
DESCRIPTION¶
List::MoreUtils provides some trivial but commonly needed functionality
on lists which is not going to go into 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.
- any BLOCK LIST
- Returns a true value if any item in LIST meets the
criterion given through BLOCK. Sets $_ for each item in LIST in turn:
print "At least one value undefined"
if any { ! defined($_) } @list;
Returns false otherwise, or if LIST is empty.
- all BLOCK LIST
- Returns a true value if all items in LIST meet the
criterion given through BLOCK, or if LIST is empty. Sets $_ for each item
in LIST in turn:
print "All items defined"
if all { defined($_) } @list;
Returns false otherwise.
- none BLOCK LIST
- Logically the negation of "any". Returns a true
value if no item in LIST meets the criterion given through BLOCK, or if
LIST is empty. Sets $_ for each item in LIST in turn:
print "No value defined"
if none { defined($_) } @list;
Returns false otherwise.
- notall BLOCK LIST
- Logically the negation of "all". Returns a true
value if not all items in LIST meet the criterion given through BLOCK.
Sets $_ for each item in LIST in turn:
print "Not all values defined"
if notall { defined($_) } @list;
Returns false otherwise, or if LIST is empty.
- 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;
- 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".
- 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".
- 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
- 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 }
- before BLOCK LIST
- Returns a list of values of LIST upto (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.
- 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 inclues the element for
which BLOCK is true.
- 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
- 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_val" is an alias for "firstval".
- 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_val" is an alias for "lastval".
- 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
- 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 retuns
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
- 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".
- uniq LIST
- distinct LIST
- Returns a new list by stripping duplicate values in LIST.
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
- 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.
- 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]
EXPORTS¶
Nothing by default. To import all of this module's symbols, do the conventional
use List::MoreUtils ':all';
It may make more sense though to only import the stuff your program actually
needs:
use List::MoreUtils qw{ any firstidx };
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.
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'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.
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=List-MoreUtils
<
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=List-MoreUtils>
THANKS¶
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 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.
TODO¶
A pile of requests from other people is still pending further processing in my
mailbox. This includes:
- •
- List::Util export pass-through
Allow List::MoreUtils to pass-through the regular List::Util
functions to end users only need to "use" the one module.
- •
- uniq_by(&@)
Use code-reference to extract a key based on which the uniqueness is
determined. Suggested by Aaron Crane.
- •
- 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
AUTHOR¶
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
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.