jtescher/descriptive-statistics

This gem calculates descriptive statistics including measures of central tendency (e.g. mean, median mode), dispersion (e.g. range, and quartiles), and spread (e.g variance and standard deviation).

descriptive-statistics's Issues

R squared, also called the square of the Pearson product-moment correlation coefficient

It will be great to calculate this as well.

Skewness breaks with an empty set

…I think. Got an Airbrake error:

NoMethodError: undefined method**' for nil:NilClass

vendor/bundle/ruby/1.9.1/gems/descriptive-statistics-1.3.0/lib/descriptive-statistics/shape.rb:6:in 'skewness'
`

Can't regenerate the data set, but your standard deviation calculation will return nil in the case of an empty set, so that should probably be caught elsewhere.

NoMethodError (undefined method `zero?' for nil:NilClass):

I just installed this on my rails 3.2.2 app and Im getting the following error:

Completed 500 Internal Server Error in 2ms

NoMethodError (undefined method `zero?' for nil:NilClass):
  app/controllers/admin_controller.rb:35:in `get_unseen_markers'

  Rendered /Users/chris/.rvm/gems/ruby-1.9.3-head@arcbs-audit-tool/gems/actionpack-3.2.2/lib/action_dispatch/middleware/templates/rescues/_trace.erb (2.7ms)
  Rendered /Users/chris/.rvm/gems/ruby-1.9.3-head@arcbs-audit-tool/gems/actionpack-3.2.2/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (1.3ms)
  Rendered /Users/chris/.rvm/gems/ruby-1.9.3-head@arcbs-audit-tool/gems/actionpack-3.2.2/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (13.0ms)

I found this when I first encountered the error and believe this might have something to do with it : http://stackoverflow.com/a/9497207/377679

standard deviation of 1 element is nil, not 0

variance does not calculate correctly

2.1.1 :015 > DescriptiveStatistics::Stats.new([1,2,3]).variance
=> 1.0

expected: 2/3