How do I find the standard deviation in Ruby?

Question

I wrote a program which looks up data in a separate txt file and then gives the average and the standard deviation. It finds my average but I get an error for Standard deviation. Was wondering anyone could help me fix my code. This is it:

data = File.open("avg_temp.txt", "r+")

contents = data.read

contents = contents.split("\r\n")
#split up array
contents.collect! do |x|
    x.split(',') 
end


sum = 0

contents.each do |x|
#make loop to find average
        sum = sum  + x[1].to_f
end
avg = sum / contents.length
puts "The average temperature of Laguardia Airport from 11/97 - 05/11 is:
#{ avg.round(3)}C (Answer is rounded to nearest thousandth place)"
#puts average


variance = 0
contents.each do |x|
        variance = variance + (x-avg)**2
end

variance = variance / contents
variance = Math.sqrt(variance)
puts variance

I get an error where it at line 27: variance = variance + (x-avg)**2

avg_temp.rb:27:in `-': can't convert Float into Array (TypeError)
    from avg_temp.rb:27:in `block in <main>'
    from avg_temp.rb:26:in `each'
    from avg_temp.rb:26:in `<main>'

Answer 1

Use

variance = variance / contents.size # or contents.length