While both of these work, neither is very good code. In the first example, you pass undef an array slice, but undef doesn't work on array slices (you're just not using undef for its designed purpose, so you don't care). It would be better to say 
@hash{@list} = ();

[download]
In the second, you use grep where a foreach is more sensible. In fact, 
1 for @hash{@list};

[download]
works just as well (you don't even have to assign anything).
Caution: Contents may have been coded under pressure.

In reply to Re^2: Adding Unique Elements to Array by Roy Johnson
in thread Adding Unique Elements to Array by thekestrel

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