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Re: reverse sort arrays in subroutines

by AnomalousMonk (Abbot)
on May 22, 2013 at 00:59 UTC ( #1034652=note: print w/ replies, xml ) Need Help??


in reply to reverse sort arrays in subroutines

JockoHelios: your reply indicates you have grasped the points others are making. However, I see a potential stumbling block looming before you.

The default ordering of sort is lexicographic-ascending (see Alphabetical order and Lexicographical order as potential starting points for info on this), and sort implicitly converts its arguments to strings for this sort and effectively compares elements with the cmp stringwise-comparison operator; see Equality Operators in perlop. However, the way you are initializing your  @TaR array suggests you are dealing with numbers rather than strings.

If you do intend to work with numbers, be aware that lexicographic sorting can produce very surprising results. Note in the example below that 10 sorts before 2 and 20 before 4 in the default sort. The solution is to supply an explicit numeric-comparison block to sort. (The <=> 'spaceship' numeric-comparison operator is also discussed in Equality Operators along with cmp.) I hope this helps.

>perl -wMstrict -le "my @TaR = (8, 2, 5, 20, 4, 10, 5, 6, 1, 8); print qq{original: @TaR}; ;; my @sorted_lex = sort @TaR; print qq{lexical: @sorted_lex}; ;; my @sorted_num = sort { $a <=> $b } @TaR; print qq{numeric: @sorted_num}; " original: 8 2 5 20 4 10 5 6 1 8 lexical: 1 10 2 20 4 5 5 6 8 8 numeric: 1 2 4 5 5 6 8 8 10 20


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Re^2: reverse sort arrays in subroutines
by JockoHelios (Scribe) on May 22, 2013 at 19:01 UTC

    Thanks to all who posted for your advice and counsel. It's gotten me past the current roadblock, and then some. Several posts were sort of prescient with regard to where I was going next, so when I checked back I had some answers I didn't know I needed. This morning, I found out I needed them :)

    Thanks again for your help.

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