this doesn't sort

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;` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l]
Re^2: this doesn't sort by hsfrey (Beadle) on Feb 26, 2012 at 06:36 UTC
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.	[reply]
Re^3: this doesn't sort by moritz (Cardinal) on Feb 26, 2012 at 06:42 UTC
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. Perl 6 - second systems done right	[reply] [d/l] [select]
Re^4: this doesn't sort by hsfrey (Beadle) on Feb 26, 2012 at 19:13 UTC


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