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Re^2: Sort Hash of Hash numerically

by duelafn (Priest)
on Jun 13, 2011 at 14:33 UTC ( #909390=note: print w/ replies, xml ) Need Help??


in reply to Re: Sort Hash of Hash numerically
in thread Sort Hash of Hash numerically

Is reverse sort optimized away (it would be cool if it swapped the meaning of $a and $b) or do you really mean:

for (sort { $HoH{$b}{head_count} <=> $HoH{$a}{head_count} } keys %HoH) + { print "$_ House Type: $HoH{$_}{house_type} Head Count: $HoH{$_}{he +ad_count}\n"; }

Update: toolic++. I went searching for the definition of "newer perls" and found that this optimization has been around for some time. From perl586delta:

reverse sort ... is now optimized to sort in reverse, avoiding the generation of a temporary intermediate list.

for (reverse @foo) now iterates in reverse, avoiding the generation of a temporary reversed list.

Good Day,
    Dean


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Re^3: Sort Hash of Hash numerically
by toolic (Chancellor) on Jun 13, 2011 at 14:50 UTC
    I really meant to use reverse. According to Perl::Critic::Policy::BuiltinFunctions::ProhibitReverseSortBlock
    Conway says that it is much clearer to use reverse than to flip $a and $b around in a sort block. He also suggests that, in newer perls, reverse is specifically looked for and optimized, and in the case of a simple reversed string sort, using reverse with a sort with no block is faster even in old perls.

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