Hi,
You can do it with by()
by(mtcars, mtcars[, "cyl"], FUN = function(d) {
c(sum = rowSums(d), mean = rowSums(d))
})
Let's say that you have your data in variable df you may use:
by(df, df[, "year"], FUN = function(d) {
c(sum = rowSums(d), mean = rowSums(d))
})
You may be interested in grouping by several columns:
by(df, df[, c("bank", "year")], FUN = function(d) {
c(sum = rowSums(d), mean = rowSums(d))
})