# How to use Enumerable

**URL:** <https://www.ruby-forum.com/t/how-to-use-enumerable/115500>\
**Category:** Ruby\
**Created:** [September 25, 2007, 8:21pm UTC](https://www.ruby-forum.com/t/how-to-use-enumerable/115500 "2007-09-25T20:21:19Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![kule](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/ecccb3/32.png) [@kule](https://www.ruby-forum.com/u/kule)\
**Post date:** [September 25, 2007, 8:21pm UTC](https://www.ruby-forum.com/t/how-to-use-enumerable/115500/1 "2007-09-25T20:21:19Z")

</div>

Hi,

Really need a little help understanding how to implement Enumerable -  
maybe I’m thinking about this the wrong way - what I’d like to do is:

sm = ScoreMatrix.new  
sm.keywords \<\< Keyword.new(1)  
sm.keywords \<\< Keyword.new(2)  
sm.keywords.sum #=\> returns 3

I currently have:

class ScoreMatrix  
def initialize  
@keywords = [] # \<= what do I put here?  
end

def keywords  
@keywords  
end  
end

class Keyword  
include Enumerable

attr\_accessor :hits

def initialize(hits)  
@hits = hits  
@array = []  
end

def sum  
total = 0  
@array.each do |item|  
total += item.hits  
end  
total  
end

def each  
@array.each do |item|  
yield item  
end  
self  
end

def add(item)  
@array.push(item)  
self  
end  
alias :\<\< :add  
end

Am I on the right track or way off? :0)

Many Thanks

Luke

---

<div class="post-metadata">

**Author:** ![kule](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/ecccb3/32.png) [@kule](https://www.ruby-forum.com/u/kule)\
**Post date:** [September 25, 2007, 9:22pm UTC](https://www.ruby-forum.com/t/how-to-use-enumerable/115500/2 "2007-09-25T21:22:45Z")

</div>

On Sep 25, 2007, at 2:21 PM, Luke P. wrote:

> I currently have:
> 
> def sum  
> end  
> Am I on the right track or way off? :0)  
> It looks to me that you are confusing a Class with an array of  
> objects of that class. It’s hard for me to see what you are trying to  
> accomplish, but to the best of my understanding, all you need is  
> following:

`
class ScoreMatrix
    attr_reader :keywords
    def initialize
       @keywords = []
    end
    def sum
       @keywords.inject(0) { |s, keywd| s += keywd.hits }
    end
end
class Keyword
attr_reader :hits
def initialize(hits)
@hits = hits
end
end
sm = ScoreMatrix.new
sm.keywords << Keyword.new(1)
sm.keywords << Keyword.new(2)
sm.sum # => 3
`

I can’t see that you need to include Enumerable in the Keyword class.  
You aren’t treating Keyword objects as collections, you are just  
iterating over an array of Keywords. Array already includes Enumerable.

Perhaps what you really want is for ScoreMatrix objects to behave as  
if _they_ were an array of Keyword hits. If that’s the case, then you  
want something like:

`
class ScoreMatrix
    include Enumerable
    attr_reader :keywords
    def initialize
       @keywords = []
    end
    def each
       @keywords.each { |keywd| yield keywd.hits }
    end
    def sum
       inject(0) { |s, h| s += h }
    end
end
class Keyword
attr_reader :hits
def initialize(hits)
@hits = hits
end
end
sm = ScoreMatrix.new
sm.keywords << Keyword.new(1)
sm.keywords << Keyword.new(2)
sm.sum # => 3
`

Regards, Morton

---

<div class="post-metadata">

**Author:** ![kule](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/ecccb3/32.png) [@kule](https://www.ruby-forum.com/u/kule)\
**Post date:** [September 26, 2007, 10:35am UTC](https://www.ruby-forum.com/t/how-to-use-enumerable/115500/3 "2007-09-26T10:35:16Z")

</div>

Thanks very much for the reply Morton,

Thats helpful I’ll do a bit of investigation into inject too!