in R, how to calculate mean of all column, by group?

Question

I need to get the mean of all columns of a large data set using R, grouped by 2 variables.

Lets try it with mtcars:

library(dplyr)
g_mtcars <- gro         


        

Answer 1

using data.table.(however you can't setDT(mtcars) because binding is locked. copy it to a different name like dt and try

 library(data.table)
 mt_dt = as.data.table(mtcars)
 mt_dt[ , lapply(.SD, mean) , by=c("cyl", "gear")]