// preformRegression performs a linear regression of create repo counts vs. day.
func performRegression(counts [][]int) *regression.Regression {
	var r regression.Regression
	r.SetObserved("count of created Github repos")
	r.SetVar(0, "days since Jan 1 2013")

	for _, count := range counts {
		r.Train(regression.DataPoint(
			float64(count[1]),
			[]float64{float64(count[0])}))
	}

	r.Run()
	return &r
}