From: "Kroeger, Simon (ext)" <simon.kroeger.ext@...>
Date: 2005-12-13T21:15:21+09:00
Subject: Re: stable sort_by?

 

> -----Original Message-----
> From: list-bounce@example.com 
> [mailto:list-bounce@example.com] On Behalf Of Frederick Ros
> Sent: Tuesday, December 13, 2005 1:01 PM
> To: ruby-talk ML
> Subject: Re: stable sort_by?
> 
> Kroeger, Simon (ext) wrote:
> 
> > Full Ack,
> > 
> > obviously sort_by isn't stable:
> > 
> > test = [[1, 'b'], [1, 'c'], [0, 'a']]
> > p test.sort_by{|t|t[0]}
> > 
> > => [[0, "a"], [1, "c"], [1, "b"]]
> > (ruby 1.8.2 (2004-12-25) [i386-mswin32])
> 
> Hummm not sure to understand ... You asked for a sort on the 
> first item 
> ... So, in this case [1,"c"] and [1,"b"] are equivalent, and 
> their order 
> is un-important ...

From http://en.wikipedia.org/wiki/Stable_sort :

Stability: stable sorting algorithms maintain the relative order 
of records with equal keys (i.e. values). That is, a sorting algorithm 
is stable if whenever there are two records R and S with the same 
key and with R appearing before S in the original list, R will appear 
before S in the sorted list.

cheers

Simon