From: gotoken@... (GOTO Kentaro)
Date: 2001-01-08T06:19:42+09:00
Subject: [ruby-talk:8784] Re: No :<, :>, etc. methods for Array

In message "[ruby-talk:8782] Re: No :<, :>, etc. methods for Array"
    on 01/01/08, "Brian F. Feldman" <green@FreeBSD.org> writes:
>I know you can define sum in terms of inject, but what is the point of 
>having inject if people are just going to use it to create sum?

Well, I think we sometimes need to write something:

  def product
    @array.inject(1){|p,i| p *= i}
  end

  def sum
    inject(element_type.induced_from(0)){|n,i| n.add!(i)}
  end

  def average_score
    @profile.inject(0){|s,i| s += i.score}/@size
  end

or

  def pipeline
    @process.inject(Product.new){|r,p| p.call(r)}
  end

So, inject seems to be not only theoretical.  Furthermore, I don't
need Array#sum so often.  On the other hand, when I need sum I need
often also average, variance or square_error{|x| model(x)}.  For
Enumerable, maybe a module `Statistics' is more useful.

Btw, I think that sum's argument for the empty case is convenient,
e.g.:

  def sum(if_empty = 0)  # Is the integer zero suitable?
    total = if_empty
    self.each {|x| total += x}
    total
  end

-- Gotoken