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in reply to Re^4: Memory Efficient Alternatives to Hash of Array
in thread Memory Efficient Alternatives to Hash of Array

You are exactly right, tilly.

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Re^6: Memory Efficient Alternatives to Hash of Array
by BrowserUk (Pope) on Dec 28, 2008 at 01:05 UTC

    I stand corrected.

    However, you're still better off using an external sort, as it allows you to gather the multiple values for each key together without loading the entire dataset into memory. Using a fairly simple loop like this:

    #! perl use strict; my( $key, @array ) = split "\t", <>; while( <> ) { chomp; my( $newKey, $value ) = split "\t"; if( $newKey eq $key ) { push @array, $value; next; } else { # Process @array for $key #... ## Remember the newKey $key = $nextKey; ## And the reset the array @array = $value; } }

    And a command line like:

    sort < unsortedFile | perl theScriptAbove

    Or just sort the file and then feed it to the script as separate steps:

    sort < unsortedFile > sortedFile perl theScriptAbove sortedFile

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      *ahem* My first answer had the same idea, but with one less bug.