Calculate days since last event in R

Question

My question involves how to calculate the number of days since an event last that occurred in R. Below is a minimal example of the data:

df <- data.frame         


        

Answer 1

It's painful and you lose performance but you can do it with a for loop :

datas <- read.table(text = "date event
2000-07-06     0
2000-09-15     0
2000-10-15     1
2001-01-03     0
2001-03-17     1
2001-05-23     1
2001-08-26     0", header = TRUE, stringsAsFactors = FALSE)


datas <- transform(datas, date = as.Date(date))

lastEvent <- NA
tae <- rep(NA, length(datas$event))
for (i in 2:length(datas$event)) {
  if (datas$event[i-1] == 1) {
    lastEvent <- datas$date[i-1]
  }
  tae[i] <- datas$date[i] - lastEvent

  # To set the first occuring event as 0 and not NA
  if (datas$event[i] == 1 && sum(datas$event[1:i-1] == 1) == 0) {
    tae[i] <- 0
  }
}

cbind(datas, tae)

date event tae
1 2000-07-06     0  NA
2 2000-09-15     0  NA
3 2000-10-15     1   0
4 2001-01-03     0  80
5 2001-03-17     1 153
6 2001-05-23     1  67
7 2001-08-26     0  95