在R中，是否有一种方法可以使用滞后时间在两个不同的列中两次获取两次之间的时间差，但忽略所有空值？

Question

I have a dataframe that looks like this:

a<-data.frame(Time = c("Time1",
                   "Time2",
                   "Time3",
                   "Time4",
                   "Time5",
                   "Time6"),
          Start = c("2018-03-17 08:38:00",
                    NA,
                    NA,
                    NA,
                    NA,
                    NA),
          End = c(NA,
                  NA,
                  NA,
                  NA,
                  NA,
                  "2018-03-17 14:31:00"))

I am trying to add another column with the time difference between the "End" time and the "Start" time.

I've tried to use difftime(End, lag(Start), units = "mins"). But I can't seem to figure out how to ignore the null values to use the last non-null value in "Start".

This is how I expect the result to look:

b<-data.frame(Time = c("Time1",
                   "Time2",
                   "Time3",
                   "Time4",
                   "Time5",
                   "Time6"),
          Start = c("2018-03-17 08:38:00",
                    NA,
                    NA,
                    NA,
                    NA,
                    NA),
          End = c(NA,
                  NA,
                  NA,
                  NA,
                  NA,
                  "2018-03-17 14:31:00"),
          Time_Diff_min = c(rep(353, times = 6)))

Thank you!

Answer 1

Apply na.locf0 to both columns and subtract.

library(zoo)
transform(a, diff = as.numeric(difftime(na.locf0(as.POSIXct(End), fromLast = TRUE), 
                                        na.locf0(as.POSIXct(Start)),
                                        unit = "min")))

giving:

   Time               Start                 End diff
1 Time1 2018-03-17 08:38:00                <NA>  353
2 Time2                <NA>                <NA>  353
3 Time3                <NA>                <NA>  353
4 Time4                <NA>                <NA>  353
5 Time5                <NA>                <NA>  353
6 Time6                <NA> 2018-03-17 14:31:00  353