How do I take a slice of a hash reference?

[entropy]

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.

Originally posted as a Categorized Question.

[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 };

[dkubb]

Another way to get a slice from a hash reference is:

my $hashref = {
  a => 1,
  b => 2,
  c => 3,
  d => 4,
};

#Pull out elements a and d from the hashref
my @slice = @$hashref{ qw(a d) };

Originally posted as a Categorized Answer.

[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};

[tachyon]

All that is wrong with your code is the parenths. Join takes a list ie: join '', (list); To give list context to your hash slice all we need to do is move the parenths as shown, this runs fine.

Note that we do not need parenths for the array at all.

my $arr =  [1,'a',2,'b'];
my $hash = {1,'a',2,'b'};
print join ':', @$arr[1,2];
print join ':',(@$hash{1,2});

tachyon

[tachyon]

Wrong button, especially with a missing </code> Scorn pours forth like a raging torrent....

All that is wrong with your code is the parenths. Join takes a list ie: join '', (list); To give list context to your hash slice all we need to do is move the parenths as shown, this runs fine.

my $arr = 1,'a',2,'b'; 
my $hash= {1,'a',2,'b'}; 
print join ':', @$arr1,2; 
print join ':',(@$hash{1,2});

Note that we do not need parenths for the array at all.

tachyon