I would like to calculate the number of days to the next meeting

Question

I would like to calculate the number of days to the next meeting given this as sample.

meetings=c("2023-06-21","2023-05-03","2023-03-22","2023-02-01","2022-12-07")
  

dates=c("2023-08-01","2023-04-01","2023-03-01","2023-02-01","2023-01-01")
  

and returning this

c(NA,32,21,0,31)

I have tried this but does not consider all meetings

as.Date(meetings)-as.Date(dates)
Time differences in days
[1] -41  32  21   0 -25

Answer 1

First transform to date with as.Date. Sort the dates then use sapply, after defining next_meeting use difftime:

meetings <- as.Date(c("2023-06-21", "2023-05-03", "2023-03-22", "2023-02-01", "2022-12-07"))
dates <- as.Date(c("2023-08-01", "2023-04-01", "2023-03-01", "2023-02-01", "2023-01-01"))

meetings <- sort(meetings)

sapply(dates, function(date) {
  next_meeting <- meetings[which(meetings >= date)][1]
  if (is.na(next_meeting)) {
    return(NA)
  } else {
    return(as.integer(difftime(next_meeting, date, units = "days")))
  }
})

output:

[1] NA 32 21  0 31