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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 ?
870
How do I add a column to a DataFrame in R? To add a new column to a dataframe in R you can use the $-operator. For example, to add the column “NewColumn”, you can do like this: dataf$NewColumn <- Values . Now, this will effectively add your new variable to your dataset.
For adding a column to a Matrix in we use cbind() function. To know more about cbind() function simply type ? cbind() or help(cbind) in R. It will display documentation of cbind() function in R documentation as shown below.
To enter an n dimension identity matrix in R we use diag (n) function. I-diag(3), this will enter a 3×3 matrix of dimension 3. Operations in Matrices: To add and subtract the matrices with same number of rows and columns.
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]) )
Methinks you are over thinking this.
a <- matrix(1:5000, nrow=100)
a <- transform(a, first10ave = colMeans(a[1:10,]))
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