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I find myself turning to Enumberable#inject more and more. It is such a powerful method, yet I rarely see it used in others' code. Here are a couple of examples of the power of inject.

Adding Facorial to All Integers

class Integer
  def factorial
    raise 'Cannot take a factorial of a negative number' if self < 0
    return 0 if self = 0
    (2..self).inject { |total, element| total * element }
  end
end

Removing Touching Matching Elements in an Array Until No Touching Elements Match( thanks Eric )

class Array
  def remove_touchers
    self.inject([]) { |final, element| final == element ? final[0..-2] : final << element }
  end
end

So, why aren't there more people using this method? Is it just forgotten? Are you using Enumberable#inject? How are you using it?