indiejoseph

from math import sqrt

def ttest(x1, x2):
	"Student's t-test for unpaired, equal variance, equal size samples."
	if len(x1) != len(x2):
		raise ValueError('unequal sample sizes')
	mx1 = sum(x1) / len(x1)
	mx2 = sum(x2) / len(x2)
	s2x1 = sum((xi - mx1)**2 for xi in x1) / (len(x1) - 1)
	s2x2 = sum((xi - mx2)**2 for xi in x2) / (len(x2) - 1)

indiejoseph

cd /usr/local
brew versions postgresql
git checkout -b postgresql-8.4.4 [some hash]
brew install postgresql
git checkout master
git branch -d postgresql-8.4.4

http://stackoverflow.com/questions/3987683/homebrew-install-specific-version-of-formula