1-dimensional Matrix is changed to a vector in R

Question

> a<-matrix(c(1:9),3,3)
> a
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9
> a[3,]*a[,3]  # I expect 1x1 matrix as resul         


        

Answer 1

This is an R FAQ. You need to do a[3,,drop = FALSE].

Answer 2

You're confusing element-by-element multiplication and matrix multiplication (see ?"*"). You want %*%:

> a[3,]%*%a[,3]
     [,1]
[1,]  150