[FIXED] How to calculate all the elements in X X^T in R?

Issue

Let X be a matrix with n rows and p columns. I want to calculate all the p times p matrices obtained by multiplying the rows of X times the transposed of the same rows. This is, the first matrix is

X[1,]%*%t(X[1,])

I want to avoid a for loop, so I wonder how to obtain the n (p times p) matrices associated to

X[i,]%*%t(X[i,])

with a more direct command such as apply or sweep. Sorry, I just cannot figure out how to do it.

Solution

You should use crossprod or tcrossprod for operations like that (see here). In your case,

lapply(1:nrow(X), function(i) tcrossprod(X[i,]))

Answered By - linog

Answer Checked By - Cary Denson (PHPFixing Admin)