I have a data frame similar to the following:
library(data.table)
test <- data.table(data.frame("value" = c(5,NA,8,NA,NA,8,6,NA,NA,10),
"locf_N" = c(1,NA,1,NA,NA,1,2,NA,NA,2)) )
In this data frame I have a variable that indicates the times I could carry forward the last observation (locf_N). This is not a fixed number for all observations. I have tried to use the maxgap parameter in the na.locf function for this purpose but it is not actually what I am looking for.
require(zoo)
test[,value := na.locf(value, na.rm = FALSE, maxgap = 1)]
test[,value := na.locf(value, na.rm = FALSE, maxgap = locf_N)]
Is there any parameter to set the number of times the last observation can be carried forward? Any ideas welcome.
Desired output:
output <- data.table(data.frame("value" = c(5,5,8,8,NA,8,6,6,6,10),
"locf_N" = c(1,NA,1,NA,NA,1,2,NA,NA,2)) )
cumsum(!is.na(value)) is a grouping vector that groups each non-NA with the following NAs. Then for each such group repeat the first value the required number of times and leave the remaining values as NA.
test[, list(value = replace(value, 1:min(.N, locf_N[1] + 1), value[1]), locf_N),
by = cumsum(!is.na(value))][, -1]
giving:
value locf_N
1: 5 1
2: 5 NA
3: 8 1
4: 8 NA
5: NA NA
6: 8 1
7: 6 2
8: 6 NA
9: 6 NA
10: 10 2