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Re^4: Memory Efficient Alternatives to Hash of Array

by tilly (Archbishop)
on Dec 27, 2008 at 21:01 UTC ( #732837=note: print w/replies, xml ) Need Help??

in reply to Re^3: Memory Efficient Alternatives to Hash of Array
in thread Memory Efficient Alternatives to Hash of Array

From the OP's text and code I thought that the OP wanted to know all of the possible values for the second field for each possible value of the first field. Given that the first field repeats, this requires an array.
  • Comment on Re^4: Memory Efficient Alternatives to Hash of Array

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Re^5: Memory Efficient Alternatives to Hash of Array
by neversaint (Deacon) on Dec 28, 2008 at 00:34 UTC
    You are exactly right, tilly.

    neversaint and everlastingly indebted.......

      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

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
        *ahem* My first answer had the same idea, but with one less bug.

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