I've gone with hdb's suggestion in the other node with the nested foreach loops but I simplified the hash definition to

I reversed the hash after reading that in perl, hashes are optimized for searching the keys, so now the \@zeros are the keys. But they're arrays, at least in my head. I'm used to thinking in terms of vectors, sets of ordered pairs, etc & not strings or whatever.

I'm interested in the keys that only contain integers so the "something" I was thinking of using a regex like this

because that would find floats with the right form. It's just I'm not sure what to put in the grep to make sure I'm getting only @zeros that have ALL integers inside & not just at least one. I wouldn't hve thought to use more than one grep like Don Coyote though. Maybe I need to learn more about grep... & then after finding a slice with the right keys, print out the corresponding values. But it's the grep part that I'm stuck on.

I do not think that reversing the hash helps. In any case you should define a function that returns true (ie 1) if the argument is (approximately) an integer and then do a grep on the \@zeroes.

# untested
sub is_approximately_an_integer {
  my $x = shift;
  my $eps = 0.0001;
  return abs( $x-round($x) ) < $eps;
}
[download]

I got an uninitialized variable error the way you had it so I added the foreach bit here, & also changed the round to int(). I got your idea:

sub is_approximately_an_integer {
    foreach my $x ( @zeros ) {
    $x = shift;
    my $eps = 0.0001;
    return abs( $x-int($x) ) < $eps;
    }
}
[download]

It seems to work ok like that. I guess next is to use the subroutine with $_ inside grep somehow?

my @wants = grep {  } values %haystack;