in reply to Hash slices

Roger has already provided a few solutions, and QM has a good answer, but here's another:

    my %newhash1 = map  { $_=>$hash{$_} }
                   grep { /^NETWORK/    }
                   keys %hash;

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I'm not sure how all these compare in terms of speed, efficiency, etc. This is just how I'd do it for greatest clarity.

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Re: Re: Hash slices
by QM (Parson) on Feb 17, 2004 at 21:56 UTC
    I tried to find an elegant way to avoid map...grep, but only came up with this: 
    my %hash2;
map { $hash2{$_} = $hash{$_} if /^NETWORK/ } keys %hash;

    [download]
    which is fancy-looking, non-map-in-a-void-context way of saying: 
    my %hash2;
{ $hash2{$_} = $hash{$_} if /^NETWORK/ } foreach keys %hash;

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    My rough check with Benchmark shows no difference between map...grep and map alone until the hash sizes were increased to force memory paging to disk.

    [I didn't check to see if anything was optimized away.]

    -QM
    --
    Quantum Mechanics: The dreams stuff is made of

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      I tried to find an elegant way to avoid map...grep

      Roger's first solution actually does this in a pretty nice way. I added some formatting to [hopefully] make it more clear, but here's his code:

          my %hashslice1 = map { /^NETWORK/
                           ? ($_, $hash{$_})
                           : (             )
                         } keys %hash;

      [download]

      Even still, I can see how mixing the selection of the keys with the hashification is a bit confusing, so that's why I gave a map {} grep {} solution that separates them.

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        Thanks!

        Need new glasses (or new eyes).

        -QM
        --
        Quantum Mechanics: The dreams stuff is made of

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