How to generate a series （1,2,2,3,3,3,4,4,4,4）
r, series
Solution
rep(1:4, 1:4)
[1] 1 2 2 3 3 3 4 4 4 4
Similarly for another series we get
rep(1:5, 1:5) * (-1)^rep(0:4, 1:5)
[1] 1 -2 -2 3 3 3 -4 -4 -4 -4 5 5 5 5 5
Problem
I am confused that how to generate a series （like this `1,2,2,3,3,3,4,4,4,4`） in R. I use the `for loop` and `rep` function like this, ``` for (i in 1:10) {rep(i,i)} ``` but I can't paste them together.