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Re: Count and List Items in a List

by perlfan (Curate)
on Nov 01, 2005 at 15:36 UTC ( #504606=note: print w/ replies, xml ) Need Help??


in reply to Count and List Items in a List

Assuming you get "results.txt" into an array, "@lists":

my %counts = (); map {$counts{$_}++} @list;
And the hash "%counts" will contain the item as a key and its count as the key's value. This is really a short version of the first post, but map is a neat function :). pF


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Re^2: Count and List Items in a List
by ikegami (Pope) on Nov 01, 2005 at 16:16 UTC

    Except map is painfully slow in void context:

    This is perl, v5.6.1 built for MSWin32-x86-multi-thread Rate map foreach map 953/s -- -25% foreach 1278/s 34% --
    This is perl, v5.8.0 built for MSWin32-x86-multi-thread Rate map foreach map 1705/s -- -25% foreach 2288/s 34% --
    This is perl, v5.8.0 built for i386-freebsd Rate map foreach map 847/s -- -29% foreach 1190/s 40% --

    This may have been fixed since.

      This is perl, v5.8.6 built for i686-linux Rate foreach map foreach 47168/s -- -2% map 48260/s 2% --

      That said, I always prefer code that does what it says and says what it does. To me, for/foreach evaluates code foreach element in a list, while map maps (or transforms) one list into another. If you want to iterate over a list, use for or foreach. If you want to transform from one list to another, use map.

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