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

Old question, but I was experimenting with rolling joins and found this interesting.

library(data.table)
setDT(df)
setkey(df, date)

# rolling self-join to attach last event time
df = df[event == 1, .(lastevent = date), key = date][df, roll = TRUE]

# find difference between record and previous event == 1 record
df[, tae := difftime(lastevent, shift(lastevent, 1L, "lag"), unit = "days")]

# difftime for simple case between date and joint on previous event
df[event == 0, tae:= difftime(date, lastevent, unit = "days")]

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