How to do Group By Rollup in R? (Like SQL)

Question

I have a dataset and I want to perform something like Group By Rollup like we have in SQL for aggregate values.

Below is a reproducible example. I k

Answer 1

melt/dcast in the reshape2 package can do subtotalling. After running dcast we replace "(all)" in the month column with the month using na.locf from the zoo package:

library(reshape2)
library(zoo)

m <- melt(df, measure.vars = "sales")
dout <- dcast(m, year + month + region ~ variable, fun.aggregate = sum, margins = "month")

dout$month <- na.locf(replace(dout$month, dout$month  == "(all)", NA))

giving:

> dout
  year month region sales
1 2016     1   east   400
2 2016     1   west   600
3 2016     1  (all)  1000
4 2017     2   east   800
5 2017     2   west  1200
6 2017     2  (all)  2000