Parse abbreviated numbers in Ruby

What's the best way in Ruby to turn human-readable abbreviated numbers into actual i开发者_如何学Gontegers?

Examples:

"1.2M" => 1200000
"477k" => 477000

---

module SIValue
  # http://en.wikipedia.org/wiki/SI_prefix
  PREFIX_MAGNITUDES = {
    'Y' =>  24, 'Z' =>  21, 'E' =>  18, 'P' =>  15, 'T'  =>  12,
    'G' =>   9, 'M' =>   6, 'k' =>   3, 'h' =>   2, 'da' =>   1,
    'd' =>  -1, 'c' =>  -2, 'm' =>  -3, 'μ' =>  -6, 'n'  =>  -9,
    'p' => -12, 'f' => -15, 'a' => -18, 'z' => -21, 'y'  => -24
  }
  def self.from( str )
    _, num, prefix = str.match(/^([-+]?[0-9]*\.?[0-9]+(?:[eE][-+]?[0-9]+)?)(#{PREFIX_MAGNITUDES.keys.join('|')})?/o).to_a
    if num
      prefix ? num.to_f * 10**PREFIX_MAGNITUDES[prefix] : num.to_f
    else
      0.0
    end
  end
end

%w[ 1k +3.3m +3.3M 123.123da 0.31h 0.31μ cats ].each do |s|
  p [s,SIValue.from(s) ]
end
#=> ["1k", 1000.0]
#=> ["+3.3m", 0.0033]
#=> ["+3.3M", 3300000.0]
#=> ["123.123da", 1231.23]
#=> ["0.31h", 31.0]
#=> ["0.31μ", 3.1e-07]
#=> ["cats", 0.0]

---

def scale s
  a = s.downcase.split /(?=[a-z])/
  Integer(a.first.to_f * Hash.new(1).merge('k' => 1024, 'm' => 1024 * 1024)[a[1]] + 0.5)
end

 # you may want to extend the hash with more suffix types