search for: tp4648000p4648013

I have a dataframe. Let's suppose that i have two columns. The first one contains height, the second one contains eye color that can be Green, Blue or Brown. I want to calculate the aritmetic mean of the height only for those people who have Blue eyes. How can I do it? Thank you for your availability. -- View this message in context: http://r.789695.n4.nabble.com/Mean-Help-tp4648000.html