stddev


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34

#!/usr/bin/env ruby

require 'trollop'

conf = Trollop::options do
  banner "stddev [-r <d>] < <one number per line>"
  opt :round, "Number of digits after decimal point.", :type => :int, :default => -1
end

sum = 0.0
i = 0
cached = []
while line=STDIN.gets
  v = line.to_f
  sum += v
  cached << v
  i +=1
end

avg = sum/i.to_f

var = 0
cached.each { |v|
  var += (avg - v)**2
}

stddev = Math.sqrt(var/i.to_f)

if conf[:round] >= 0
  puts stddev.round conf[:round]
else
  puts stddev
end