How to use Enumerable

[Luke Pearce]

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

 

[Morton Goldberg]

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)

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:

<code>
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
</code>

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:

<code>
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
</code>

Regards, Morton