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Re^2: "Just use a hash": An overworked mantra?

by blakew (Monk)
on Nov 17, 2011 at 18:00 UTC ( #938657=note: print w/ replies, xml ) Need Help??


in reply to Re: "Just use a hash": An overworked mantra?
in thread "Just use a hash": An overworked mantra?

"An array on the other hand can only be used when your data is an integer"

I think you meant "maps 1:1 with integers."


Comment on Re^2: "Just use a hash": An overworked mantra?
Re^3: "Just use a hash": An overworked mantra?
by Tux (Monsignor) on Nov 17, 2011 at 18:38 UTC

    In this case, "data" is a bunch of integers. In moving from a hash to an array, the "keys" do have to be integers. I you're just counting, nothing else matters, but if it is about key-value pairs, that move is still valid if just the key is a (positive) integer. The value(s) in that pair do not have to be.

    Another thing not yet mentioned is that with datasets this large, not only the data itself may put a limit on the internal available memory footprint, but the overhead in perl structures add to that. Just today I checked what the internal representation of a 1 Mb .csv file was represented as an array(ref) of array(ref)s: it grew to 10Mb! A hash takes slightly more overhead than an array (most overhead goes into converting a single number into a refcounted SV), so when on the verge of swapping, an array might actually be much faster than a hash.


    Enjoy, Have FUN! H.Merijn
      Your data can be characters; in which case use ord to map to integers for the key. The point is your data just needs to be mappable to integers, not necessary integers themselves.

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