You could also refer to the very complete Getting Matching Items From An Array.

At first I said, "of course GrandFather is right", but upon further testing the situation is not so clear. The optimizations in grep give it an edge over the C style for if you have to look approximately 1/2 way into the array. This did not surprise me as much as the poor performance of a binary search. ( code borrowed from Binary search). Though I think after struggling to coax grep to return a list value into a scalar context I would avoid that solution unless you really want multiple values returned.

oko1 gives an implementation of grep but I was thinking more something like: grep {$array[$_] eq $value} (0..$#array) as shown in the code below. Which, as I said, may be just quick enough.

#!/usr/bin/perl

use Benchmark 'cmpthese';
use warnings;

@array = (  'a'..'zz' );
$value = 'mz';
my $res;
my $position;

print "for(): ".traditional().
      "\tforeach: ".for_each().
      "\tmap: ".maptohash().
      "\tgrep_if: ".grep_if().
      "\tbinary search: ".bin_search().
"\n";

cmpthese ( 1000, { for_loop =>  '$res = traditional()',
                       map => '$res = maptohash()',
                  for_each => '$res = for_each()',
                   grep_if => '$res = grep_if()',
                bin_search => '$res = bin_search()',
                }
 );

sub traditional{
    for ($position=0; $position <= $#array; $position++) {
        last if ($array[$position] eq $value);
    }
    return $position;
}

sub for_each{
    for  our $position ( 0..$#array ) {
        last if ($array[$position] eq $value) ;
    }
    return $position;
}

sub maptohash{
    %indexed = map{ $array[$_], $_ } (0..$#array);
    return $indexed{$value};
}

sub grep_if{
    my  @res = grep {$array[$_] eq $value} (0..$#array);
   return @res[0];
}

sub bin_search {
    return BinSearch( $value, \&cmpFunc, \@array );
}

sub BinSearch
{
my ($target, $cmp) = @_;
my @array = @{$_[2]};

my $posmin = 0;
my $posmax = $#array;

return -0.5 if &$cmp (0, \@array, $target) > 0;
return $#array + 0.5 if &$cmp ($#array, \@array, $target) < 0;

while (1)
  {
  my $mid = int (($posmin + $posmax) / 2);
  my $result = &$cmp ($mid, \@array, $target);

  if ($result < 0)
    {
    $posmin = $posmax, next if $mid == $posmin && $posmax != $posmin;
    return $mid + 0.5 if $mid == $posmin;
    $posmin = $mid;
    }
  elsif ($result > 0)
    {
    $posmax = $posmin, next if $mid == $posmax && $posmax != $posmin;
    return $mid - 0.5 if $mid == $posmax;
    $posmax = $mid;
    }
  else
    {
    return $mid;
    }
  }
}

sub cmpFunc
{
my ($index, $arrayRef, $target) = @_;
my $item = $$arrayRef[$index];

return $item cmp $target;
}


 %perl foo.pl                                                         
+    [10:49pm]
Scalar value @res[0] better written as $res[0] at foo.pl line 47.
for(): 363      foreach: 363    map: 363        grep_if: 363    binary
+ search: 363
             Rate        map   for_loop    grep_if bin_search   for_ea
+ch
map         200/s         --       -69%       -72%       -81%       -8
+8%
for_loop    650/s       224%         --        -8%       -39%       -6
+0%
grep_if     707/s       253%         9%         --       -33%       -5
+7%
bin_search 1058/s       428%        63%        50%         --       -3
+6%
for_each   1641/s       719%       153%       132%        55%         
+--

[download]

s//----->\t/;$~="JAPH";s//\r<$~~/;{s|~$~-|-~$~|||s |-$~~|$~~-|||s,<$~~,<~$~,,s,~$~>,$~~>,, $|=1,select$,,$,,$,,1e-1;print;redo}

In reply to Re: Finding values position in array by starbolin
in thread Finding values position in array by cosmicperl

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