From: Robert Klemme <shortcutter@...>
Date: 2012-01-23T19:43:41+09:00
Subject: Re: uniq with count; better way?

On Mon, Jan 23, 2012 at 11:15 AM, Karsten Meier
<developer@handylearn-projects.de> wrote:
> If your data items are integers, and from a rather small range (compared
> to computer memory...), then you can use an array instead of an hash:
>
> maxval = 10
> result = Array.new(maxval+1, 0)
> ar.each{
>  |x| result[x] += 1;
> }
>
> This returns an array and not an hash.
> [0, 0, 0, 0, 2, 2, 3, 1, 0, 0, 0]
>
> To make a histogram, that data structure is even better. Otherwise you
> need to transform it to a hash again. But for large data sets I still
> expect it  to be faster:

Don't expect, measure.  There's Benchmark...

> Your cpu  does not need to calculate a hash key of every single data
> item, because the data item is already a perfect key for the array. Also
> no hash key collisions can occur.

But if only few of the numbers in the range are used you waste a
potentially large Array for just a few entries.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/