How to group by a fixed number of rows in dplyr?

Question

I have a data frame:

set.seed(123)
x <- sample(10)
y <- x^2
my.df <- data.frame(x, y)

The result is this:

> my.         


        

Answer 1

We can use rep or gl to create the grouping variable

library(dplyr)
my.df %>% 
    group_by(grp = as.integer(gl(n(), 5, n()))) %>% 
    #or with rep
    # group_by(grp = rep(row_number(), length.out = n(), each = 5)) 
    summarise(sum = sum(y), mean = mean(y))
# A tibble: 2 x 3
#    grp   sum  mean
#    
#1     1   174  34.8
#2     2   211  42.2