in reply to Efficient random hash stuff

Ah, no need to splice. 

# @keys = keys %hash;  # done ONCE
# ($k,$v) = rhe(%hash,@keys);

sub rhe (\%\@) {
    my( $hv, $av )= @_;
    my $idx= rand @$av;
    my $key= $av->[$idx];
    my $val= delete $hv->{$key};
    my $last= pop @$av;
    $av->[$idx]= $last   if  $idx < @$av;
    return( $key, $val );
}

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As for saving space, I don't see you really making use of the hash here so you could do: 

@keys = keys %hash;
@vals = values %hash;
undef %hash;

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If the keys are long, then you could also probably save a bit of space by storing reference to the keys in the array instead of the key values themself (or maybe not).

        - tye (but my friends call me "Tye")

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Re: (tye)Re: Efficient random hash stuff
by japhy (Canon) on Nov 17, 2000 at 01:28 UTC
    Wow, that's damn nice. And we could use my just-an-array idea from above: 
    sub rand_element (\@);

@array = ([1,2], [3,4], [5,6]);  # etc...
($k,$v) = rand_element(@array);

sub rand_element (\@) {
  my $aref = shift;
  my $idx = rand @$aref;
  my ($k,$v) = @{ $aref->[$idx] };
  my $last = pop @$aref;
  $aref->[$idx] = $last if $idx < @$aref;
  return ($k,$v);
}

    [download]
    Thank you muchly, tye. I need to ++ YOU, not your node...

    $monks{japhy}++ while $posting;
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[d/l]

      Note that ([1,2],[3,4],[5,6],...) consumes quite a bit more memory (no, I haven't tested this) than ( [1,3,5,...], [2,4,6,...] ). I agree that this is less elegant, but if memory usage is a primary concern, then the elegance loss might be worth it.

              - tye (but my friends call me "Tye")
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[select]
        Ok, modified thus: 
        sub rand_element (\@);

@array = ([1,3,5], [2,4,6]);  # [keys], [values]
($k,$v) = rand_element(@array);

sub rand_element (\@) {
  my $aref = shift;
  my $idx = rand @{$aref->[0]};
  my ($k,$v) = ($aref->[0][$idx], $aref->[1][$idx]);
  my @last = (pop @{$aref->[0]}, pop @{$aref->[1]});
  ($aref->[0][$idx],$aref->[1][$idx]) = @last
    if $idx < @{$aref->[0]};
  return ($k,$v);
}

        [download]
        While not tested, I do belive it works -- the code has been changed only to allow for the different structure.

        Thanks again, tye/Tye.

        $monks{japhy}++ while $posting;
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