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#!/usr/bin/env ruby
require 'trollop'
def usage
STDERR.write "./stddev [-r <d>] < <one number per line>\n"
exit 1
end
usage if not [0,2].include? ARGV.size
opts = Trollop::options do
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.strip.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)
if opts[:round] >= 0
puts stddev.round opts[:round]
else
puts stddev
end
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