From: dblack@...
Date: 2006-01-04T22:24:15+09:00
Subject: Re: Newbie question about nested sort

Hi --

On Wed, 4 Jan 2006, Grehom wrote:

> what am I doing wrong?  I wanted to sort primarily on count (second
> position in array), then sub-sort alphabetically (first position in
> array)
>
> char_freq = [["c", 2],["b", 5],["a", 2]]
> sorted_freq = char_freq.sort {|a, b| b[1]<=>a[1] || a[0]<=>b[0] }
> sorted_freq.each do |d|
>   print d[0]*d[1]
> end
>
> produces >>  bbbbbccaa
>
> when I was rather hoping for >> bbbbbaacc

Since 0 is true in Ruby (unlike Perl, where it's false), the || test
will never be performed, because b[1] <=> a[1] is always true.

You can use sort_by, though:

   sorted_freq = char_freq.sort_by {|a| [-a[1], a[0]] }

(You can also do explicit tests for a 0 result, but sort_by is much
more concise.)


David

-- 
David A. Black
dblack@wobblini.net

"Ruby for Rails", from Manning Publications, coming April 2006!
http://www.manning.com/books/black