Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks! ok - i'm experimenting with hashes and want to be able to look for the presence of certain keys in a hash and then simply print the corresponding values to those keys. Hope someone can help! 

my @array = ('sarah', 'john');  # stores the keys i'm interested in
my %hash = (
            'sarah' => '19',
            'john' => '25',
            'emma' => '22',
            );


if (exists ($hash{$array[0]}))  {

    print value;

}

[download]

Replies are listed 'Best First'.
•Re: extracting values from hashes
by merlyn (Sage) on Mar 18, 2003 at 13:49 UTC
    Given that you spoke only abstractions, like "array" and "hash", I would suspect this is homework.

    However, you access the value of a hash in the same way you used exists. So you were mostly there.

    -- Randal L. Schwartz, Perl hacker
    Be sure to read my standard disclaimer if this is a reply.

[reply]
Re: extracting values from hashes
by broquaint (Abbot) on Mar 18, 2003 at 13:55 UTC 
    my @array = qw/sarah john/;
my %hash  = (
  sarah => 19,
  john  => 25,
  emma  => 22,
);
print "$_: $hash{$_}\n" for grep exists $hash{$_}, @array;

__output__

sarah: 19
john: 25

    [download]
    See. exists and grep for more info.
    HTH

    _________
    broquaint

[reply]
[d/l]
      thanks for your help broquaint, this makes sense, but how would it be possible to push the information on the print line into an array as the following doesn't work; 
      
push @data, "$_: $hash{$_}\n" for grep exists $hash{$_}, @array;

      [download]
[reply]
[d/l]
        If you just want the array elements that exists as keys in the hash, a simple grep() should do the job. 
        my @array = qw/sarah john/;
my %hash  = (
  sarah => 19,
  john  => 25,
  emma  => 22,
);
## push() would be superfluous
my @data = grep exists $hash{$_}, @array;

print "data: @data\n";

__output__

data: sarah john

        [download]

        HTH

        _________
        broquaint

[reply]
[d/l]

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