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From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: Sorting an associative array by value?
Message-ID: <1991Apr05.193734.20851@convex.com>
Date: 5 Apr 91 19:37:34 GMT
References: <1991Apr5.183701.21325@javelin.sim.es.com>
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Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
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From the keyboard of pashdown@javelin.sim.es.com (Pete Ashdown):
:How do I go about sorting an associative array, not by the string, but by
:the associated value?  For example, how would I change following 'word count'
:program to sort by occurance rather than alphabetically?
:
:foreach $word (sort keys(%wordcount)) {
:	printf "%20s %d\n", $word, $wordcount{$word};
:}

The most straight-forward way is to declare a function that 
given keys, compares values.  For example:

    sub by_value { $wordcount{$a} <=> $wordcount{$b}; } 

    foreach $word (sort by_value keys %wordcount) {
	    printf "%20s %d\n", $word, $wordcount{$word};
    }

A minor problem with this method is that the array to compare
is hardcoded in.  You can avoid this by using dynamic scoping.
I'll also use pass-by-name for efficiency.

    sub _by_value { $table{$a} <=> $table{$b}; } 

    sub sort_by_value {
	local(*table) = @_;
	sort _by_value keys %table;
    } 

    foreach $word (&sort_by_value(*wordcount)) {
	    printf "%20s %d\n", $word, $wordcount{$word};
    }

Another possibilty, which I don't care for as much, is to dynamically
declare the &by_value function using an eval.  This is left as
an exercise for the reader.  :-)

I guess I'd better keep the sorting section in my perl 
tutorial after all.

--tom