From: Phrogz <gavin@...>
Date: 2006-09-06T03:45:11+09:00
Subject: Modifying the first value with #inject

Is there an idiom for doing something to the first value as part of an
inject? Or do I need to .map{}.inject{}?

class Array
  def sum
    inject(0){ |total, entry| total + entry.to_f }
  end
  def product
    inject(1){ |total, entry| total * entry.to_f }
  end
  def running_difference
    inject{ |total, entry| total - entry.to_f }
  end
  def running_divide
    inject{ |total, entry| total / entry.to_f }
  end
end

a1 = [5,4,3,2,1]
p a1.sum
#=> 15.0
p a1.product
#=> 120.0
p a1.running_difference
#=> -5.0
p a1.running_divide
#=> 0.208333333333333

a2 = ["5","4","3","2","1"]
p a2.sum
#=> 15.0
p a2.product
#=> 120.0
p a2.running_difference
#=> tmp.rb:9:in `running_difference': undefined method `-' for
"5":String (NoMethodError)
#=> 	from tmp.rb:36:in `inject'
#=> 	from tmp.rb:9:in `running_difference'
#=> 	from tmp.rb:31