[SOLVED] Fill missing Variables by Information from other date columns (R)

Fill missing Variables by Information from other date columns (R)

I have a Dataframe which looks similar to this:

set.seed(42)   
start <- Sys.Date() + sort(sample(1:10, 5))
set.seed(43)
end <-  Sys.Date() + sort(sample(1:10, 5))
end[4] <- NA
A <- c("10", "15", "NA", "4", "NA")
B  <- rpois(n = 5, lambda = 10) 
df <- data.frame(start, end, A, B)

I would like , when there is an NA in the column A to caclulate the hours beweet start and end. Nothing shall happen when either start or end is NA.

I tried somthing like that:

df[, df$A [is.na(df[, df$A])]] <- difftime(df$end, df$start, units =  "hours")

but this gives me the Error: undefined columns selected.

Does someone have an Idea? Thanks.

Solution

Create an index where there are NA in 'A' column, subset the 'start', 'end' based on the index, get the difftime and assign back

df$A <- as.numeric(df$A)
i1 <- is.na(df$A)
df$A[i1] <-  with(df, as.numeric(difftime(start[i1], end[i1], units = "hours")))