R编程 - 在现有矩阵中添加额外的列

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.

randomMatrix <- generateMatrix(1,5000,100,50)
randomMatrix51 <- matrix(nrow=100, ncol=1)

for(ctr in 1:ncol(randomMatrix)){  
randomMatrix51.mat[1,ctr]  <- sum(randomMatrix [ctr, 1:10])/10
}

This gives the below error

Error in randomMatrix51.mat[1, ctr] <- sum(randomMatrix[ctr, 1:10])/10 :incorrect
number of subscripts on matrix

I tried this

cbind(randomMatrix,sum(randomMatrix [ctr, 1:10])/10)

But it only works for one row, if I use this cbind in the loop all the old values are over written.

How do I add the average of first 10 values in the new column. Is there a better way to do this other than looping over rows ?

Answer 1

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]) )

Answer 2

Methinks you are over thinking this.

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