From: Mathieu Bouchard <matju@...>
Date: 2000-12-02T07:32:05+09:00
Subject: [ruby-talk:6723] Re: Array Intersect (&) question

> >Use a hash.  Here's code to do both and more.  It assumes that
> >each element is unique in a given array:
> >    @union = @intersection = @difference = ();
> >    %count = ();
> >    foreach $element (@array1, @array2) { $count{$element}++ }
> >    foreach $element (keys %count) {
> >        push @union, $element;
> >        push @{ $count{$element} > 1 ? \@intersection : \@difference },
> >$element
> >;
> >    }
> Wow! Much faster than the standard Ruby Array#&. Thanks much (I'll check 
> there myself for these sorts of questions from now on).

I translated the above code into Ruby. If you run the code below, Array#&
becomes quite faster than the above code.

class Array; def &(other)
        union = []
        inter = []
        diff = []
        count = {}
        (self+other).each {|x| count[x] = 1 + count.fetch(x) {0}}
        count.each_key {|x|
                union << x
                (count[x] > 1 ? inter : diff) << x
        }
        inter
end end



matju