Given two arrays (with duplicates), one a proper subset of the other, produce a third array containing those in the first not in the second. Eg. 

my @a = (43,43,44);
my @b = (43,43);
## Required result
my @c = (44);

my @p = ( 1,1,1,1,1,2,2,2,3,3,4,5,6);
my @q = ( 1,2,3,4,5,6 );
## Required result
my @r = ( 1,1,1,1,2,2,3 );

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The FAQ solution produces both intersection and difference, and more than doubles memory usage in the process.

List::Compare more than quadruples memory usage on it's way to calculating about fifty things I don't need as well as the one I do.

Most of the other CPAN and Categorised answer solutions don't handle duplicates, use large amounts of memory, or both.

Is there a simple variation on a using a hash and grep that works? Cos I'm not seeing it written anywhere and its eluding me.

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In reply to Difference arrays. by BrowserUk

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