Doguu introduce arithmetic mean, geometric mean, harmonic mean and dispersion. Reference is https://www.utp.or.jp/book/b300857.html .
Run below command on shell.
gem install doguubundle exec rake specrequire 'doguu'
Doguu.arithmetic_mean([1, 2, 3]) # => 2.0
Doguu.geometric_mean([1.1, 1.05, 1.03]) # => 1.06
Doguu.harmonic_mean([20, 30]) # => 24.0
Doguu.variance([5, 6, 7, 7, 10]) # => 2.8