http://www.perlmonks.org?node_id=73550

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

Is there a method for directly retrieving the size of a hash, or must I use an array? 
%somehash = ( key1 => "value1",
              key2 => "value2",
              key3 => "value3,
              key4 => "value4",
             );
@keys = keys %somehash;
$size = @keys;
print "This hash holds $size key-value pairs\n";

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Replies are listed 'Best First'.
Re: hash size
by davorg (Chancellor) on Apr 18, 2001 at 20:14 UTC
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[d/l]
Re: hash size
by arturo (Vicar) on Apr 18, 2001 at 20:17 UTC

    "size of a hash" isn't really well defined. You can get the number of keys, or the number of values pretty easily. (does a key w/o a defined value count? It might not for some purposes). You can cut down the keystrokes on your method with something like the following: 

    print "This hash holds ". scalar keys %somehash . " keys\n";

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    HTH 

    perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n";*other_name = *rose;print "$other
+_name\n"'

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[reply]
[d/l]
[select]
Re: hash size
by larsen (Parson) on Apr 18, 2001 at 20:54 UTC
    Another point from perldata. It could be useful for a certain definition of size :)...
    If you evaluate a hash in a scalar context, it returns a value which is true if and only if the hash contains any key/value pairs. (If there are any key/value pairs, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash. This is pretty much useful only to find out whether Perl's (compiled in) hashing algorithm is performing poorly on your data set. For example, you stick 10,000 things in a hash, but evaluating %HASH in scalar context reveals "1/16", which means only one out of sixteen buckets has been touched, and presumably contains all 10,000 of your items. This isn't supposed to happen.)
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Re: hash size
by zigster (Hermit) on Apr 18, 2001 at 20:18 UTC
    Not really AFAIC. You can shorten things sumwhat by calling keys in scalar context: 
    
%somehash = ( key1 => "value1",
              key2 => "value2",
              key3 => "value3,
              key4 => "value4",
             );
$size = keys %somehash;
print "This hash holds $size key-value pairs\n";

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    --

    Zigster
[reply]
[d/l]

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