From: Christoph <chr_news@...>
Date: 2002-03-20T11:01:34+09:00
Subject: Re: Why is Ruby so slow? - Solution

"Venherm Borchers" <Venherm.Borchers@t-online.de> wrote in
....
> The solution
> ------------
>
> Nobu Nakada pointed out that the following line might be causing the
> problem, and it indeed does:
>
>         nitms = (@col[j]-['']).nitems
>
> Here I relied on the 'set difference' that returns an array of only
> unique elements which then are counted. I have to warn you: this kind
> of set operation is _unbelievably_ slow!

This depends. If you ``set subtract'' a one million element set from an
other one million element set then the current Array#- implementation
will be unbelievably fast.
Your problem is probably the picture perfect example that the price
tag for the convenience of  ``mixin in'' the functionality of a HashSet
class into a list like Array class are the occasional severe performance
penalties - this kind thing would have never happened if you had been
forced to write out the ``hidden type conversions'' explicitly.

/Christoph