[R] Taking the sum of only some columns of a data frame

[Mathew Guilfoyle]

This does the summation you want in one line:

#create example data and column selection
d = as.data.frame(matrix(rnorm(50),ncol=5))
cols = c(1,3)

#sum selected columns and put results in new row
d[nrow(d)+1,cols] = colSums(d[,cols])

However, I would agree with the sentiments that this is a bad idea; far better to have the mean values stored in a new object leaving the original data table untainted.  


> On 31 Mar 2017, at 17:20, Bruce Ratner PhD <br at dmstat1.com> wrote:
> 
> Hi R'ers:
> Given a data.frame of five columns and ten rows. 
> I would like to take the sum of, say, the first and third columns only.
> For the remaining columns, I do not want any calculations, thus rending their "values" on the "total" row blank. The sum/total row is to be combined to the original data.frame, yielding a data.frame with five columns and eleven rows. 
> 
> Thanks, in advance. 
> Bruce 
> 
> 
> ______________
> Bruce Ratner PhD
> The Significant Statistician™
> 
> 
> 
> 
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