> NOTE: when i contains duplicates, by=.EACHI is different to by=key(DT); e.g, ```R setkey(DT, ID) ids = c("id1", "id2", "id1") DT[ids, sum(val), by = ID] # 2 rows returned DT[ids, sum(val), by = .EACHI] # 3 rows, in the order of ids (result 1 and ...
How to remove a column in r Supposed you want to drop columns in an R dataframe by name. You can accomplish this by the simple act of setting that specific column to NULL, as demonstrated by the drop function code below. # how to remove a column in r / delete column in R # this ...