From: "(r.*n){2}" <perl2ruby@...>
Date: 2010-09-28T11:55:09+09:00
Subject: Re: Space Ship Operator <=> Odd Behaviour

On Sep 27, 10:13 pm, Nathanial Allan <nathanial.al...@gmail.com>
wrote:
> I have come across a strange occurance when I use the space ship
> operator to compare percentages.
>
> I want to compare percentages to see if they are greater than, less than
> or equal to 85%, this mostly works fine - all the way up to 99% - it
> returns a 1 obviously meaning that 99% is greater than 85%
>
> however the strangeness comes in when I attempt to compare 100% or
> greater against 85% - it returns -1
>
> I am fairly new to ruby - by no means an expert so I suspect there is
> something wrong with what I am doing rather than the spaceship operator.
> Can someone please shine some light on this for me so that I may better
> understand.
>
> I have the knowledge to perform this operation another way with differnt
> code, but I am interested to know why - if there is a logical
> explaination.
>
> Thanks in advance!
> --
> Posted viahttp://www.ruby-forum.com/.

that is because the sort being performed is alphanumeric instead of
numeric. In the example below, z has the correct sorted values. Due to
the way to_i is defined, '10%'.to_i is same as '10'.to_i.

x = [ '35%', '25%', '5%', '10%', '100%', '15%' ]
y = x.sort { |a,b| a <=> b }
z = x.sort { |a,b| a.to_i <=> b.to_i }
puts "x is:"
p x
puts "y is:"
p y
puts "z is:"
p z

Output:
x is:
["35%", "25%", "5%", "10%", "100%", "15%"]
y is:
["10%", "100%", "15%", "25%", "35%", "5%"]
z is:
["5%", "10%", "15%", "25%", "35%", "100%"]