This (basically exact same as yours) code works for me (prints "k1\nk2\n") -- what is a sample of your <FILE>?: 
use strict;
use warnings;
my %hash = map {
     (split /:/, $_ )[0] => (split /:/, $_ )[2]
    } <DATA>;
print join ( "\n", sort keys %hash ) . "\n";
__DATA__
k1:asd:v1
k2:asd:v2

[download]
One suggestion though, would be to change the map so that the split() is only done once (no functionality change, just for efficiency): 
  map {
    my @tmp = split /:/, $_;
    $tmp[0] => $tmp[2];
  } <FILE>

[download]
(could also do map { (split(/:/, $_)) [0,2] } but that's not as clear that it's key/value pairs)
Update: Oops. I see now that OP said he won't be using the two splits....

In reply to Re: Problem generating a hashtable by davidrw
in thread Problem generating a hashtable by Tomtom

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