It looks like we were both wrong. None of them are equivalent. ;)

use strict;
use warnings;
use Data::Dumper;

my %hash;

while(<DATA>){
#chomp;
  $hash{$_}++ for split;  
}

$hash{''}=2;

print Dumper(\%hash);
print '*'x55,"\n";

my @greparr=  grep {$hash{$_} > 1} sort keys %hash;
print "greparr has ", scalar @greparr, " elements.\n";

my @maparr = map {$_ if $hash{$_} > 1} sort keys %hash;
print "maparr has ", scalar @maparr, " elements.\n";

my @grep2 = grep {$_ if $hash{$_} > 1} sort keys %hash;
print "grep2 has ", scalar @grep2, " elements.\n";

print '*'x55,"\n";
print Dumper(\@greparr);
print '*'x55,"\n";
print Dumper(\@maparr);
print '*'x55,"\n";
print Dumper(\@grep2);
print '*'x55,"\n";

__DATA__
0 0
teacher students
teacher students
nope

[download]

Output:

$VAR1 = {
          '' => 2,
          '0' => 2,
          'nope' => 1,
          'students' => 2,
          'teacher' => 2
        };
*******************************************************
greparr has 4 elements.
maparr has 5 elements.
grep2 has 2 elements.
*******************************************************
$VAR1 = [
          '',
          '0',
          'students',
          'teacher'
        ];
*******************************************************
$VAR1 = [
          '',
          '0',
          '',
          'students',
          'teacher'
        ];
*******************************************************
$VAR1 = [
          'students',
          'teacher'
        ];
*******************************************************

[download]

In reply to Re^4: why use a hash instead of an array by Lotus1
in thread why use a hash instead of an array by DarrenSol

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