Fill NA in a time series only to a limited number

Question

Is there a way we can fill NAs in a zoo or xts object with limited number of NAs forward. In other words like fill

Answer 1

From playing around in data.table comes this hacky solution:

np1 <- 3 + 1
dt[, 
   x_filled := x[c(rep(1, min(np1, .N)), rep(NA, max(0, .N - np1)))],
   by = cumsum(!is.na(x))]
# Or slightly simplified:
dt[, 
   x_filled := ifelse(rowid(x) < 4, x[1], x[NA]),
   by = cumsum(!is.na(x))]

> dt
          date  x x_filled
 1: 2019-02-14  1        1
 2: 2019-02-15 NA        1
 3: 2019-02-16 NA        1
 4: 2019-02-17 NA        1
 5: 2019-02-18  5        5
 6: 2019-02-19 NA        5
 7: 2019-02-20 NA        5
 8: 2019-02-21 NA        5
 9: 2019-02-22 NA       NA
10: 2019-02-23 NA       NA
11: 2019-02-24 11       11
12: 2019-02-25 12       12
13: 2019-02-26 NA       12
14: 2019-02-27 NA       12
15: 2019-02-28 NA       12
16: 2019-03-01 NA       NA
17: 2019-03-02 NA       NA
18: 2019-03-03 NA       NA
19: 2019-03-04 19       19
20: 2019-03-05 20       20

We build on the fact that subsetting vectors with NA returns NA.

Data/Packages

library(zoo)
library(data.table)
x <- zoo(1:20, Sys.Date() + 1:20)
x[c(2:4, 6:10, 13:18)] <- NA
dt <- data.table(date = index(x), x = as.integer(x))