Subversion Repositories an-fpga-implementation-of-low-latency-noc-based-mpsoc

package List::MoreUtils;

use 5.008_001;

use strict;

use warnings;

my $have_xs;

our $VERSION = '0.430';

BEGIN

{

    unless (defined($have_xs))

    {

        ## no critic (ErrorHandling::RequireCheckingReturnValueOfEval)

        eval { require List::MoreUtils::XS; } unless $ENV{LIST_MOREUTILS_PP};

        ## no critic (ErrorHandling::RequireCarping)

        die $@ if $@ && defined $ENV{LIST_MOREUTILS_PP} && $ENV{LIST_MOREUTILS_PP} == 0;

        $have_xs = 0 + defined($INC{'List/MoreUtils/XS.pm'});

    }

    use List::MoreUtils::PP qw();

}

use Exporter::Tiny qw();

my @junctions = qw(any all none notall);

my @v0_22     = qw(

  true false

  firstidx lastidx

  insert_after insert_after_string

  apply indexes

  after after_incl before before_incl

  firstval lastval

  each_array each_arrayref

  pairwise natatime

  mesh uniq

  minmax part

  _XScompiled

);

my @v0_24  = qw(bsearch);

my @v0_33  = qw(sort_by nsort_by);

my @v0_400 = qw(one any_u all_u none_u notall_u one_u

  firstres onlyidx onlyval onlyres lastres

  singleton bsearchidx

);

my @v0_420 = qw(arrayify duplicates minmaxstr samples zip6 reduce_0 reduce_1 reduce_u

  listcmp frequency occurrences mode

  binsert bremove equal_range lower_bound upper_bound qsort

  slide slideatatime);

my @all_functions = (@junctions, @v0_22, @v0_24, @v0_33, @v0_400, @v0_420);

## no critic (TestingAndDebugging::ProhibitNoStrict)

no strict "refs";

if ($have_xs)

{

    my $x;

    for (@all_functions)

    {

        List::MoreUtils->can($_) or *$_ = $x if ($x = List::MoreUtils::XS->can($_));

    }

}

List::MoreUtils->can($_) or *$_ = List::MoreUtils::PP->can($_) for (@all_functions);

use strict;

## use critic (TestingAndDebugging::ProhibitNoStrict)

use parent qw(Exporter::Tiny);

my %alias_list = (

    v0_22 => {

        first_index => "firstidx",

        last_index  => "lastidx",

        first_value => "firstval",

        last_value  => "lastval",

        zip         => "mesh",

    },

    v0_33 => {

        distinct => "uniq",

    },

    v0_400 => {

        first_result  => "firstres",

        only_index    => "onlyidx",

        only_value    => "onlyval",

        only_result   => "onlyres",

        last_result   => "lastres",

        bsearch_index => "bsearchidx",

    },

    v0_420 => {

        bsearch_insert => "binsert",

        bsearch_remove => "bremove",

        zip_unflatten  => "zip6",

    },

);

our @EXPORT_OK   = (@all_functions, map { keys %$_ } values %alias_list);

our %EXPORT_TAGS = (

    all         => \@EXPORT_OK,

    'like_0.22' => [

        any_u    => {-as => 'any'},

        all_u    => {-as => 'all'},

        none_u   => {-as => 'none'},

        notall_u => {-as => 'notall'},

        @v0_22,

        keys %{$alias_list{v0_22}},

    ],

    'like_0.24' => [

        any_u    => {-as => 'any'},

        all_u    => {-as => 'all'},

        notall_u => {-as => 'notall'},

        'none',

        @v0_22,

        @v0_24,

        keys %{$alias_list{v0_22}},

    ],

    'like_0.33' => [

        @junctions,

        @v0_22,

        # v0_24 functions were omitted

        @v0_33,

        keys %{$alias_list{v0_22}},

        keys %{$alias_list{v0_33}},

    ],

);

for my $set (values %alias_list)

{

    for my $alias (keys %$set)

    {

        ## no critic (TestingAndDebugging::ProhibitNoStrict)

        no strict qw(refs);

        *$alias = __PACKAGE__->can($set->{$alias});

        ## use critic (TestingAndDebugging::ProhibitNoStrict)

    }

}

use strict;

=pod

=head1 NAME

List::MoreUtils - Provide the stuff missing in List::Util

=head1 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';

=head1 DESCRIPTION

B<List::MoreUtils> provides some trivial but commonly needed functionality on

lists which is not going to go into L<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.

=head1 EXPORTS

=head2 Default behavior

Nothing by default. To import all of this module's symbols use the C<: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.

=head2 Like version 0.22 (last release with original API)

This API was available from 2006 to 2009, returning undef for empty lists on

C<all>/C<any>/C<none>/C<notall>:

    use List::MoreUtils ':like_0.22';

This import tag will import all functions available as of version 0.22.

However, it will import C<any_u> as C<any>, C<all_u> as C<all>, C<none_u> as

C<none>, and C<notall_u> as C<notall>.

=head2 Like version 0.24 (first incompatible change)

This API was available from 2010 to 2011.  It changed the return value of C<none>

and added the C<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 C<any_u> as C<any>, C<all_u> as C<all>, and

C<notall_u> as C<notall>.  It will import C<none> as described in

the documentation below (true for empty list).

=head2 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 C<any>, C<all>, and C<notall>.  It added the C<sort_by> and C<nsort_by> functions

and the C<distinct> alias for C<uniq>.  It omitted C<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 C<bsearch> for consistency with the 0.33 API.

=head1 FUNCTIONS

=head2 Junctions

=head3 I<Treatment of an empty list>

There are two schools of thought for how to evaluate a junction on an

empty list:

=over

=item *

Reduction to an identity (boolean)

=item *

Result is undefined (three-valued)

=back

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

In the second case, three-value logic is desired, in which a junction

applied to an empty list returns C<undef> rather than true or false

Junctions with a C<_u> suffix implement three-valued logic.  Those

without are boolean.

=head3 all BLOCK LIST

=head3 all_u BLOCK LIST

Returns a true value if all items in LIST meet the criterion given through

BLOCK. Sets C<$_> for each item in LIST in turn:

  print "All values are non-negative"

    if all { $_ >= 0 } ($x, $y, $z);

For an empty LIST, C<all> returns true (i.e. no values failed the condition)

and C<all_u> returns C<undef>.

Thus, C<< all_u(@list) >> is equivalent to C<< @list ? all(@list) : undef >>.

B<Note>: because Perl treats C<undef> as false, you must check the return value

of C<all_u> with C<defined> or you will get the opposite result of what you

expect.

=head3 any BLOCK LIST

=head3 any_u BLOCK LIST

Returns a true value if any item in LIST meets the criterion given through

BLOCK. Sets C<$_> for each item in LIST in turn:

  print "At least one non-negative value"

    if any { $_ >= 0 } ($x, $y, $z);

For an empty LIST, C<any> returns false and C<any_u> returns C<undef>.

Thus, C<< any_u(@list) >> is equivalent to C<< @list ? any(@list) : undef >>.

=head3 none BLOCK LIST

=head3 none_u BLOCK LIST

Logically the negation of C<any>. Returns a true value if no item in LIST meets

the criterion given through BLOCK. Sets C<$_> for each item in LIST in turn:

  print "No non-negative values"

    if none { $_ >= 0 } ($x, $y, $z);

For an empty LIST, C<none> returns true (i.e. no values failed the condition)

and C<none_u> returns C<undef>.

Thus, C<< none_u(@list) >> is equivalent to C<< @list ? none(@list) : undef >>.

B<Note>: because Perl treats C<undef> as false, you must check the return value

of C<none_u> with C<defined> or you will get the opposite result of what you

expect.

=head3 notall BLOCK LIST

=head3 notall_u BLOCK LIST

Logically the negation of C<all>. Returns a true value if not all items in LIST

meet the criterion given through BLOCK. Sets C<$_> for each item in LIST in

turn:

  print "Not all values are non-negative"

    if notall { $_ >= 0 } ($x, $y, $z);

For an empty LIST, C<notall> returns false and C<notall_u> returns C<undef>.

Thus, C<< notall_u(@list) >> is equivalent to C<< @list ? notall(@list) : undef >>.

=head3 one BLOCK LIST

=head3 one_u BLOCK LIST

Returns a true value if precisely one item in LIST meets the criterion

given through BLOCK. Sets C<$_> for each item in LIST in turn:

    print "Precisely one value defined"

        if one { defined($_) } @list;

Returns false otherwise.

For an empty LIST, C<one> returns false and C<one_u> returns C<undef>.

The expression C<one BLOCK LIST> is almost equivalent to

C<1 == true BLOCK LIST>, except for short-cutting.

Evaluation of BLOCK will immediately stop at the second true value.

=head2 Transformation

=head3 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 C<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 }

=head3 insert_after BLOCK VALUE LIST

Inserts VALUE after the first item in LIST for which the criterion in BLOCK is

true. Sets C<$_> 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

=head3 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

=head3 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 C<$a>

and C<$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

=head3 mesh ARRAY1 ARRAY2 [ ARRAY3 ... ]

=head3 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

C<zip> is an alias for C<mesh>.

=head3 zip6

=head3 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]

C<zip_unflatten> is an alias for C<zip6>.

=head3 listcmp ARRAY0 ARRAY1 [ ARRAY2 ... ]

Returns an associative list of elements and every I<id> of the list it

was found in. Allows 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] )

=head3 arrayify LIST[,LIST[,LIST...]]

Returns a list consisting 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

=head3 uniq LIST

=head3 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"

C<distinct> is an alias for C<uniq>.

B<RT#49800> can be used to give feedback about this behavior.

=head3 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

=head3 duplicates LIST

Returns a new list by stripping values in LIST occurring 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 more than once

in LIST.

  my @y = duplicates 1,1,2,4,7,2,3,4,6,9; #returns 1,2,4

=head3 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,...)

=head3 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]);

=head3 mode LIST

Returns the modal value of LIST. In scalar context, just the modal value

is returned, in list context all probes occurring I<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

=head3 slide BLOCK LIST

The function C<slide> operates on pairs of list elements like:

  my @s = slide { "$a and $b" } (0..3);

  # @s = ("0 and 1", "1 and 2", "2 and 3")

The idea behind this function is a kind of magnifying glass that is moved

along a list and calls C<BLOCK> every time the next list item is reached.

=head2 Partitioning

=head3 after BLOCK LIST

Returns a list of the values of LIST after (and not including) the point

where BLOCK returns a true value. Sets C<$_> for each element in LIST in turn.

  @x = after { $_ % 5 == 0 } (1..9);    # returns 6, 7, 8, 9

=head3 after_incl BLOCK LIST

Same as C<after> but also includes the element for which BLOCK is true.

=head3 before BLOCK LIST

Returns a list of values of LIST up to (and not including) the point where BLOCK

returns a true value. Sets C<$_> for each element in LIST in turn.

=head3 before_incl BLOCK LIST

Same as C<before> but also includes the element for which BLOCK is true.

=head3 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 { $idx[$i++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]

=head3 samples COUNT LIST

Returns a new list containing COUNT random samples from LIST. Is similar to

L<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;

=head2 Iteration

=head3 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 'C<index>', then it returns

the index of the last fetched set of values, as a scalar.

=head3 each_arrayref LIST

Like each_array, but the arguments are references to arrays, not the

plain arrays.

=head3 natatime EXPR, LIST

Creates an array iterator, for looping over an array in chunks of

C<$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

=head3 slideatatime STEP, WINDOW, LIST

Creates an array iterator, for looping over an array in chunks of

C<$windows-size> items at a time.

The idea behind this function is a kind of magnifying glass (finer

controllable compared to L</slide>) that is moved along a list.

Example:

  my @x = ('a' .. 'g');

  my $it = slideatatime 2, 3, @x;

  while (my @vals = $it->())

  {

    print "@vals\n";

  }

This prints

  a b c

  c d e

  e f g

  g

=head2 Searching

=head3 firstval BLOCK LIST

=head3 first_value BLOCK LIST

Returns the first element in LIST for which BLOCK evaluates to true. Each

element of LIST is set to C<$_> in turn. Returns C<undef> if no such element

has been found.

C<first_value> is an alias for C<firstval>.

=head3 onlyval BLOCK LIST

=head3 only_value BLOCK LIST

Returns the only element in LIST for which BLOCK evaluates to true. Sets

C<$_> for each item in LIST in turn. Returns C<undef> if no such element

has been found.

C<only_value> is an alias for C<onlyval>.

=head3 lastval BLOCK LIST

=head3 last_value BLOCK LIST

Returns the last value in LIST for which BLOCK evaluates to true. Each element

of LIST is set to C<$_> in turn. Returns C<undef> if no such element has been

found.

C<last_value> is an alias for C<lastval>.

=head3 firstres BLOCK LIST

=head3 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 C<$_> in turn. Returns

C<undef> if no such element has been found.

C<first_result> is an alias for C<firstres>.

=head3 onlyres BLOCK LIST

=head3 only_result BLOCK LIST

Returns the result of BLOCK for the first element in LIST for which BLOCK

evaluates to true. Sets C<$_> for each item in LIST in turn. Returns

C<undef> if no such element has been found.

C<only_result> is an alias for C<onlyres>.

=head3 lastres BLOCK LIST

=head3 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 C<$_> in turn. Returns

C<undef> if no such element has been found.

C<last_result> is an alias for C<lastres>.

=head3 indexes BLOCK LIST

Evaluates BLOCK for each element in LIST (assigned to C<$_>) and returns a list

of the indices of those elements for which BLOCK returned a true value. This is

just like C<grep> only that it returns indices instead of values:

  @x = indexes { $_ % 2 == 0 } (1..10);   # returns 1, 3, 5, 7, 9

=head3 firstidx BLOCK LIST

=head3 first_index BLOCK LIST

Returns the index of the first element in LIST for which the criterion in BLOCK

is true. Sets C<$_> 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 C<-1> if no such item could be found.

C<first_index> is an alias for C<firstidx>.

=head3 onlyidx BLOCK LIST

=head3 only_index BLOCK LIST

Returns the index of the only element in LIST for which the criterion

in BLOCK is true. Sets C<$_> 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 C<-1> if either no such item or more than one of these

has been found.

C<only_index> is an alias for C<onlyidx>.

=head3 lastidx BLOCK LIST

=head3 last_index BLOCK LIST

Returns the index of the last element in LIST for which the criterion in BLOCK

is true. Sets C<$_> 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 C<-1> if no such item could be found.

C<last_index> is an alias for C<lastidx>.

=head2 Sorting

=head3 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.

=head3 nsort_by BLOCK LIST

Similar to sort_by but compares its key values numerically.

=head3 qsort BLOCK ARRAY

This sorts the given array B<in place> using the given compare code. Except for

tiny compare code like C<< $a <=> $b >>, qsort is much faster than Perl's C<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