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Learning Ruby: Exercise #1

I've just finished exercise #1 from: Please feel free to critique this code, I am serious about learning Ruby and getting introduced to members of the community.


# Write a program that takes as its arguments one of the words ’sum’,
# ‘product’, ‘mean’, or ’sqrt’ followed by a series of numbers. The
# program applies the appropriate function to the series.

# the mathn library makes the Math.sqrt call below behave better in
# situations involving negative sums.
require 'mathn'

class Array
  def sum
    # missed the inject method on my first
    # skim of the 'Programming Ruby' appendix.
    self.inject {|sum, i| sum + i}.to_f
  def product
    self.inject(1) {|product, i| product * i}.to_f
  def mean
    self.sum / self.size
  def sqrt

raise "usage: ruby proj1.rb {sum|product|mean|sqrt} {value}+" if ARGV.size < 2

Allowed_commands = ["sum", "product", "mean", "sqrt"]
command = ARGV.shift.downcase
raise "unknown command: #{command}" unless Allowed_commands.include? command

# I don't like this line, is there a better
# way to do String -> numeric conversions?
ARGV.collect! {|i| i.to_f}
puts eval ARGV.to_s + "." + command


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