DTplyWithTotals: Compute on subgroups and subtotals using data.table instead...
In sachsmc/rreporttools: A small set of tools for performing common reporting tasks

This function takes a data table, subsets it according to the levels of one or more variables, and returns a data table containing the results computed on each subset, in addition to results computed on aggregate groups. See ddplyWithTotals for an alternative.

1	DTplyWithTotals(DT, variables, EXPR, nestedOnly = FALSE, grandTotal = FALSE)

`DT`	data.table object to subset. Does not require a key, see data.table.
`variables`	Vector of character strings denoting variables to split on. Variables must be factors.
`EXPR`	An expression that indicates what to do with each subset of the data table
`nestedOnly`	Logical. Compute subtotals only for nested groups.
`grandTotal`	Logical. Compute the grand total.

mtcars2 <- data.table(mtcars, key = c("cyl", "gear"))
mtcars2[, cyl := as.factor(cyl)]
mtcars2[, gear := as.factor(gear)]
DTplyWithTotals(mtcars2, c("cyl", "gear"), list(mean = mean(wt)), grandTotal = TRUE)