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How do I take a slice of a hash reference?

by entropy (Sexton)
on May 15, 2001 at 03:17 UTC ( #80399=categorized question: print w/replies, xml ) Need Help??
Contributed by entropy on May 15, 2001 at 03:17 UTC
Q&A  > references


I can take a slice of an array ref, but not of a hash ref:
my $arr =[1,'a',2,'b']; my $hash={1,'a',2,'b'}; print join ':',(@$arr )[1,2]; print join ':',(@$hash){1,2};
The first print statement works, the second is a syntax error. I also have this problem when taking a slice of an anonymous hash:
print join ':',(1,'a',2,'b')[1,2]; print join ':',(1,'a',2,'b'){1,2};
Again, the first statement works, but the second is a syntax error.

Answer: How do I take a slice of a hash reference?
contributed by japhy

Here's how:

@slice = @{$array_ref}[ @idx ]; @slice = @{$hash_ref}{ @keys };
And there's no easy way to "pretend" a list is a hash. You need to use a hash reference explicitly:
$scalar = {1, 'a', 2, 'b'}->{$key}; @slice = @{ { 1, 'a', 2, 'b' } }{ @keys };
Answer: How do I take a slice of a hash reference?
contributed by tianping

japhy has answered the question, but it's also worth pointing out the solution to the syntax error in your original code. The parentheses alter the priority; so just remove them:

print join ':', @$hash{1,2};
More generally, put curly braces around the hash ref expression:
print join ':', @{$hash}{1,2};

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