From: Logan Capaldo <logancapaldo@...>
Date: 2006-10-12T12:14:05+09:00
Subject: Re: Counting Frequency of Values in an Array (And Sorting by Frequency?)

On Thu, Oct 12, 2006 at 11:52:19AM +0900, x1 wrote:
> Is there no method for an array that will tell me the # of occurrences
> for an item?
> 
> IE:  ["a", "a", "a", "b", "c", "c"].count("a") #producing 3 ?
> 
array.select { |i| i == 'a' }.length
or array.inject(0) { |count, item| count += 1 if item == 'a'; count }

> I almost thought that rindex would do the trick when looking at the
> class docs but.. the example was just engineered to trick me  :-(
> 
> I realize I could pass these to a block and count but.. wanted to make
> sure it didn't exist. If not, why? Thank you.. ( I did search btw.. no
> avail )
> 
> Also, what's the best way of printing out each unique item and the
> number of times it occurs, sorted by numerically by the number of
> times it occurs?
> 
> IE: in my example above, i'd like to see (sorted by occurrence
> greatest to least)
> #desired output:
> a: 3
> c: 2
> b: 1
> 
> 
> Or sorted from least to greatest:
> #desired output:
> b: 1
> c: 2
> a: 3
> 
> I was able to hack it by using a hash doing various things to it.. but
> it didn't seem "rubyish".
> 
As you say:
puts array.inject(Hash.new(0)) { |hash, item| hash[item] += 1
  hash }.sort_by { |k, v| v }.map { |k, v| "#{k}:#{v}" }
> Thank you for any input.