R programming - Adding extra column to existing matrix

Question

I am a beginner to R programming and am trying to add one extra column to a matrix having 50 columns. This new column would be the avg of first 10 values in that row.

Answer 1

Methinks you are over thinking this.

a <- matrix(1:5000, nrow=100)
a <- transform(a,  first10ave = colMeans(a[1:10,]))

Answer 2

Bam!

a <- matrix(1:5000, nrow=100)
a <- cbind(a,apply(a[,1:10],1,mean))

On big datasets it is however faster (and arguably simpler) to use:

cbind(a, rowMeans(a[,1:10]) )