How to reorder data.table columns (without copying)
One may find it easier to use the above solution, but instead sort by column number. For example: library(data.table)
> x <- data.table(a = 1:3, b = 3:1, c = runif(3))
> x
a b c
[1,] 1 3 0.2880365
[2,] 2 2 0.7785115
[3,] 3 1 0.3297416
> setcolorder(x, c(3,2,1))
> x
c b a
[1,] 0.2880365 3 1
[2,] 0.7785115 2 2
[3,] 0.3297416 1 3
Use setcolorder()
:
library(data.table)
x <- data.table(a = 1:3, b = 3:1, c = runif(3))
x
# a b c
# [1,] 1 3 0.2880365
# [2,] 2 2 0.7785115
# [3,] 3 1 0.3297416
setcolorder(x, c("c", "b", "a"))
x
# c b a
# [1,] 0.2880365 3 1
# [2,] 0.7785115 2 2
# [3,] 0.3297416 1 3
From ?setcolorder
:
In
data.table
parlance, allset*
functions change their input by reference. That is, no copy is made at all, other than temporary working memory, which is as large as one column.
so should be pretty efficient. See ?setcolorder
for details.