如何找到红宝石的平均值和标准偏差？

Question

我编写了一个程序，它可以找到一个单独的 txt 文件中的大型数据集的平均值和标准偏差。我希望这个程序可以处理任何数据集。我通过输入两个简单的数据点（与温度相关的年份和月份）来测试我的程序：

2009-11,20 2009-12,10

运行它时，它说我的平均值是 20，标准差是 0（显然是错误的）。

这是我的程序：

data = File.open("test.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 of your large data set is: #{ avg.round(3)} (Answer is rounded to nearest thousandth place)"
#puts average

#similar to finding average, this finds the standard deviation
variance = 0
contents.each do |x|
  variance = variance + (x[1].to_f - avg)**2
end

variance = variance / contents.length
variance = Math.sqrt(variance)
puts "The standard deviation of your large data set is:#{ variance.round(3)} (Answer is rounded to nearest thousandth place)"

Answer 1

我认为问题来自使用 \r\n 拆分数据，这取决于操作系统：如果您使用的是 Linux，则应该是 contents.split('\n')。无论哪种方式，您最好使用IO#each 遍历文件中的每一行并让Ruby 处理行结束字符。

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

count = 0
sum = 0
variance = 0

data.each do |line|
  value = line.split(',')[1]
  sum = sum  + value.to_f
  count += 1
end

avg = sum / count
puts "The average of your large data set is: #{ avg.round(3)} (Answer is rounded to nearest thousandth place)"

# We need to get back to the top of the file
data.rewind

data.each do |line|
  value = line.split(',')[1]
  variance = variance + (value.to_f - avg)**2
end

variance = variance / count
variance = Math.sqrt(variance)
puts "The standard deviation of your large data set is: #{ variance.round(3)} (Answer is rounded to nearest thousandth place)"