Calculate the mean by group

Question

I have a large data frame that looks similar to this:

df <- data.frame(dive = factor(sample(c("dive1","dive2"), 10, replace=TRUE)),
            


        

Answer 1

Adding alternative base R approach, which remains fast under various cases.

rowsummean <- function(df) {
  rowsum(df$speed, df$dive) / tabulate(df$dive)
}

Borrowing the benchmarks from @Ari:

10 rows, 2 groups

10 million rows, 10 groups

10 million rows, 1000 groups