1. In the interests of efficient coding, rewrite the nested loop example below, where the matrix foo was filled with the multiples of the elements of loopvec1 and loopvec2, using only a single for loop.

R> foo <- matrix(NA,length(loopvec1),length(loopvec2)) R> foo 

[,1] [,2] [,3] [,4] [1,] NA NA NA NA [2,] NA NA NA NA [3,] NA NA NA NA R> for(i in 1:length(loopvec1)){ + for(jin1:i){ + foo[i,j] <- loopvec1[i]+loopvec2[j] +} +} R> foo

 [,1] [,2] [,3] [,4] [1,] 14 NA NA NA 

[2,] 15 14 NA NA [3,] 16 15 14 NA