Imagine one has a table X, with 10 columns Col1 - Col5. Col5 is column with amounts. With setDT I can compute the sum of Col5 over the unique Col1-Col4 combinations:
by = .(Col1,Col2,Col3,Col4)]
Is there a way to prevent having to list every Col1-4 in the by statement and instead for instance use a vector that identifies all the group by columns?
This for instance doesn't work for obvious reasons:
by = .(colnames(X[,-c(5)]))]
I don't want to use the aggregate function because it turns everything in factors.