From: nobu.nokada@...
Date: 2002-03-19T11:24:03+09:00
Subject: Re: Why is Ruby so slow?

Hi,

At Tue, 19 Mar 2002 03:41:31 +0900,
Venherm Borchers wrote:
> WHY IS RUBY SO SLOW?
> 
> I implemented a _DataReader_ class in Ruby and Python. The reader:
(snip)
> Here are the running times for some available Ruby implementations
> under Windows:
> 
>         ________data items______1,600,000_________320,000_______
> 
> Ruby 1.6.5-2                    17:10 min          46 sec
> Ruby 1.6.6-0                    18:43 min          58 sec
> Ruby 1.7.2 (i586-mswin32)       18:05 min          54 sec

tData.load ran in 2.824 secs, but tData.prelyze spent 48.655
secs, it's exactly too slow.

> def prelyze(logging=false, missing=@missing)
>     t1 = Time.now
>     dtypes = {0 => 'NA', 1 => 'Integer', 2 => 'Continuous',
>               3 => 'String', 4 => 'Set'}
>     @dtypes = []
>     for j in (0...@ncols) do
>         ctype = 0; mitms = 0
>         @col[j].each { |item|
>             if item == missing
>                 ctype = [ctype, 0].max
>                 mitms += 1
>             elsif item =~ /^\s*[+\-]?\d+\s*$/
>                 ctype = [ctype, 1].max
>             elsif item =~ /^\s*[+\-]?(?:\d+\.\d*|\d*\.\d+)\s*$/
>                 ctype = [ctype, 2].max
>             else
>                 ctype = [ctype, 3].max
>             end
>         }
> 
>         nitms = (@col[j]-['']).nitems

Possibly here.  Array#- makes a hash once so a little
expensive.  Try with:

        nitms = @col[j].nitems - @col.grep(/^$/).nitems

Or it may be better to count nitms up in @col[j].each block.

-- 
Nobu Nakada