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Re^3: Removing elemets from an array

by karlgoethebier (Curate)
on Dec 30, 2012 at 11:58 UTC ( #1010912=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Removing elemets from an array
in thread Removing elemets from an array

This is very interesting. But for the moment i don't have any idea why it is so.

Perhaps some of the involved brothers would like to comment/interprete the result so we can learn something new?

Best regards, Karl

«The Crux of the Biscuit is the Apostrophe»


Comment on Re^3: Removing elemets from an array
Re^4: Removing elemets from an array
by Lotus1 (Chaplain) on Dec 30, 2012 at 16:44 UTC

    Thanks for setting up the benchmark in the first place, it has been fun seeing the performance of the different approaches.

    Nested loops don't scale well. When there were only 2 items for the outer loop it was really fast. I've seen folks here toss around the Big O notation and although I hadn't heard of it before Perlmonks I figured out they were talking about linear growth as opposed to exponential or some other function for the execution time related to the size of the data set.

    The nested loop approach seems to be O(n^2) but I'm still learning so hopefully someone will weigh in if I'm off base.

      Thank you and HNY.

      Best regards, Karl

      «The Crux of the Biscuit is the Apostrophe»

Re^4: Removing elemets from an array (optimization)
by LanX (Canon) on Dec 30, 2012 at 17:15 UTC
    Every operation in Perl - like any abstraction - has an overhead which can't be compensated by its C-implementation.

    So tending to use as few as possible perl-commands which do mass-operations means to reduce overhead and delaying the task to highly optimized C.

    Loops (including maps) are just multiplying the amount of executed commands (just imagine the linearized alternative which is even faster as the loop...)

    so my approach is the fastest because its basically reduced to only 3 perl commandsą

    1. setting a hash

    2. deleting a slice from that hash

    3. reading the resulting hash

    OTOH my approach has drawbacks, depending on the task, it's only suitable for real sets of strings.

    Arrays can contain repeated data or other datatypes like refs.

    EDIT: you might be interested in Using hashes for set operations...

    Cheers Rolf

    PS: of course there are still loops working under the hood, but they are already optimized in C.

      ThanX - and especially for the link

      HNY and best regards, Karl

      «The Crux of the Biscuit is the Apostrophe»

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