rollapply with “growing” window

Question

Guys, normally when you do something like:

tmp = zoo(rnorm(100), 1:100)
rollapply(tmp, 10, function(x) quantile(x, 0.05), align=\"right\")

Answer 1

Why not just pad the series with 9 NAs at the beginning? Definitely better than "ugly for loops":

tmp = zoo(c(rep(NA,9), rnorm(100)), 1:109)
zoo(rollapply(tmp, 10, function(x) quantile(x, 0.05, na.rm = TRUE), 
              align="right"), 1:100)

Answer 2

rollapply in zoo can do that by specifying partial=TRUE, e.g.

> library(zoo)
> 
> rollapplyr(zoo(1:20), 3, sum, partial=TRUE)
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 
 1  3  6  9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57