For integers, this will beat using hashes hands-down: 

@a1 = map int( rand 1e6 ), 1 .. 8000; 
@a2 = map int( rand 1e6 ), 1 .. 6000;;

vec( $vec, $_, 1 )=1 for @a2;;

@missingFromA2 = grep !vec( $vec, $_, 1 ), @a1;;

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A note of caution, if the integers can be bigger than say 2**30, then this won't work properly on older perls; and would consume large amounts of memory on newer perls. But if your integers are less than that, it is very, very fast.

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In reply to Re^5: Best method to diff large array by BrowserUk
in thread Best method to diff very large array efficiently by newbieperlperson

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