Re: calculate average from range of hash values (optimize)

I don't see the need to sort all the keys in %{$data}. You can use hash slices and List::Utils::sum() to good advantage.

use List::Utils 'sum';
sub average {
    my ($data, $first, $last) = @_;
    my %data = %$data;
    my @goodkeys = grep {exists $data{$_}} $first .. $last;
    sum( @data{ @goodkeys } ) / @goodkeys;
}
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After Compline,
Zaxo

Comment on Re: calculate average from range of hash values (optimize) Download Code

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Re^2: calculate average from range of hash values (optimize) by Aristotle (Chancellor) on Jul 27, 2003 at 02:12 UTC
Nor do you need to make a copy of the hash. `use List::Util qw(sum); sub average { my ($data, $first, $last) = @_; my @goodkeys = grep exists $data->{$_}, $first .. $last; sum( @{$data}{@goodkeys} ) / @goodkeys; }` [download] Finally, that we're doing math on the values without checking their definedness suggests that valid values are never undef, in which case you can skip the double lookup. `use List::Util qw(sum); sub average { my ($data, $first, $last) = @_; my @values = grep defined, @{$data}{$first .. $last}; sum(@values) / @values; }` [download] That should be about as fast as you can get in Perl. Makeshifts last the longest.	[reply] [d/l] [select]
Re: Re^2: calculate average from range of hash values (optimize) by demerphq (Chancellor) on Jul 27, 2003 at 13:59 UTC
For the record your second solution corrupts the hash with keys whose value is undef. While the OP didnt explicitly say this was bad, I believe it was implicit in the comment that the keys could be very large or very small. Thus a search could inadverdantly create millions of keys and overflow available RAM. --- demerphq _{<Elian> And I do take a kind of perverse pleasure in having an OO assembly language...}	[reply] [d/l]
Re^4: calculate average from range of hash values (optimize) by Aristotle (Chancellor) on Jul 27, 2003 at 18:32 UTC
For the record your second solution corrupts the hash with keys whose value is undef. Eh? Extraordinarily strange. So a slice lookup autovivifies elements, while a single-element lookup doesn't. Feels like a bug, if you ask me.. certainly counterintuitive. Easy enough to fix, though. `use List::Util qw(sum); sub average { my ($data, $first, $last) = @_; my @values = map { local $_ = $data->{$_}; defined() ? $_ : () } $ +first .. $last; sum(@values) / @values; }` [download] Makeshifts last the longest.	[reply] [d/l]