R: matrix by vector multiplication

Question

I have following problem:

myvec <- c(1:3)

mymat <- as.matrix(cbind(a = 6:15, b = 16:25, c= 26:35))
mymat
       a  b  c
 [1,]  6 16 26
 [2,]  7 17 27         


        

Answer 1

An alternative, but longer way can be this one:

rowSums(t(apply(mymat, 1, function(x) myvec*x)),na.rm=T)

Is the only way that I found that can ignore NA's inside the matrix.

Answer 2

The %*% operator in R does matrix multiplication:

> mymat %*% myvec
      [,1]
 [1,]  116
 [2,]  122
 ...
[10,]  170

Answer 3

Matrices are vectors in column major order:

 colSums(  t(mymat) * myvec )  

(Edited after hopefully reading question correctly this time.)