in reply to Determing the indice of an array

One further thought. If you really do need to look up an array index from its value using a reverse lookup hash, then it might be better to use the address of the array element rather than the element itself as the hash key, which neatly avoids the problem of duplicates. 

my @a = ('a'..'d','a'..'d')
print @a;
a b c d a b c d
my %a; @a{\(@a)} = 0..$#a;
print %a;
SCALAR(0x1bd5220) 2 SCALAR(0x1bd5208) 7 SCALAR(0x1bd299c) 5 SCALAR(0x1
+bdf15c) 1 
SCALAR(0x1bd5268) 6 SCALAR(0x1bd52c8) 0 SCALAR(0x1bd53b8) 3 SCALAR(0x1
+bd2984) 4
for (@a) { 
    print "$_ has an index of $a{\$_}\n"; 
}
a has an index of 0
b has an index of 1
c has an index of 2
d has an index of 3
a has an index of 4
b has an index of 5
c has an index of 6
d has an index of 7

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Re: Re: Determing the indice of an array
by Dr. Mu (Hermit) on Mar 11, 2003 at 04:42 UTC
    That's fine if you're actually using elements of @a for the lookup, but that rather presupposes that you know where they are to begin with, doesn't it? How about this case?
    my @a = ('a'..'d','a'..'d');
my %a; @a{\(@a)} = 0..$#a;
my $x = 'b';
print "$x has an index of $a{\$x}\n";

b has an index of

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    Better for the most general case would be to make a lookup hash keyed by the values of the array, with each value of the hash being a reference to an array to which you push the indices from the original array. That way, when you key the hash with an array value, you get every location in the array where that value occurred.
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