How to reorder data.table columns (without copying)?

Question

I'd like to reorder columns in my `data.table` `x`, given a character vector of column names, `neworder`: library(data.table) x <- data.table(a = 1:3, b = 3:1, c = runif(3)) neworder <- c("c", "b", "a")Obviously I could do: x[ , neworder, with = FALSE] # or x[ , ..neworder] # c b a # 1: 0.8476623 3 1 # 2: 0.4787768 2 2 # 3: 0.3570803 1 3but that would require copying the entire dataset again. Is there another way to do this?

Answer 1

Yes, there is. After running your provided code for loading the "data.table" library, creating the x variable, and creating the neworder variable, you can reorder the columns of x without copying the entire dataset again with the following code statement:

setcolorder(x,neworder)

The preceding code statement reorders the columns of x by reference, which means that the entire dataset was not copied again as desired. The following website link provides the documentation for the R function "setcolorder":

https://www.rdocumentation.org/packages/data.table/versions/1.15.4/topics/setcolorder