There is no information in a hash with index values that isn't in an array.

Yes and no. If you want to know "the position of a given number", the information is there in the array, but finding it is hard (O(N)). It's O(1) with a hash. 

my ($index) = grep $code[$_] == $x, 0..$#code;

   -vs-

my $index = $code{$x};

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In reply to Re^4: Convert a string into a hash by ikegami
in thread Convert a string into a hash by vitoco

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