Calculate correlation by aggregating columns of data frame

Question

I have the following data frame:

y <- data.frame(group = letters[1:5], a = rnorm(5) , b = rnorm(5), c = rnorm(5), d = rnorm(5) )

How to

Answer 1

You're almost there: you just need to use apply instead of sapply, and remove unnecessary columns.

apply(y[-1], 1, function(x) cor(x[1:2], x[3:4])

Of course, the correlation between two length-2 vectors isn't very informative....