Sort rows in data.table (R)
Let's say I have the following data.table in R:
library(data.table) DT = data.table(x=rep(c("b","a","c"),each=3), y=c(1,3,6), v=1:9)
I want to order it by two columns (say columns x and v). I used this:
DT[order(x,v)] # sorts first by x then by v (both in ascending order)
But now, I want to sort it by x (in decreasing order) and have the following code:
DT[order(-x)] #Error in -x : invalid argument to unary operator
Therefore, I think this error is due to the fact that class(DT$x)=character. Could you give me any suggestion in order to solve this issue?
I know I can use DT[order(x,decreasing=TRUE)], but I want to know the syntax to sort by several columns using both ways (some decreasing, some increasing) at the same time.
Note that if you use DT[order(-y,v)] the result is ok, but if you use DT[order(-x,v)] there is an error. So, my question is: how to solve this error?
data.table now supports OP's original attempt and the following answer is no longer necessary.
You can use DT[order(-rank(x), y)].
x y v 1: c 1 7 2: c 3 8 3: c 6 9 4: b 1 1 5: b 3 2 6: b 6 3 7: a 1 4 8: a 3 5 9: a 6 6