The former compiles to a much smaller op tree than the latter:

perl -MO=Concise -e'delete @hash1{keys %hash2}'
perl -MO=Concise -e'delete $hash1{$_} for keys %hash2'

[download]

On my machine, the slice performs about 20% faster than the loop.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re^2: how do I efficiently remove one hash from another? by tobyink
in thread how do I efficiently remove one hash from another? by perltux

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