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

I have an array of arrays. I want to sort the arrays based on one element, with index $sortNdx. The following code compiles OK, but doesn't do anything. The array is left unchanged. Any suggestions as to why? 
@sorted = sort {$bigArray[$a][$sortNdx] <=> $bigArray[$b][$sortNdx]} @
+bigArray;
@bigArray = @sorted;

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Re: this doesn't sort
by BrowserUk (Patriarch) on Feb 26, 2012 at 01:51 UTC

    Use:

    @bigArray = sort { $a->[$sortNdx] <=> $b->[$sortNdx] } @bigArray;

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      Yes, That did it perfectly! :-) Thank you!

      But I don't understand it! I can't even make syntactic sense out of it. :-(

      I tried replacing $a->[$sortNdx] with [$a][$sortNdx], which I thought would be syntactically the same thing, but got a syntax error.

      Could you explain to me what's going on?

      Thanks.

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        Inside the sort block, $a and $b are elements of @bigArray, not indexes into it.

        So if @bigArray contains array refs, both $a and $b end up being an array ref. And you can dereference and index into an array with the $a->[$index] syntax.

        On the other hand if you write [$a], you wrap the array ref in $a into another array ref -- not what you want.

        See perlreftut and perlref for more details.

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