In R, is there a way to calculate the number of days between the end of one event and the beginning of another?

Question

( Note: Hotel data used as illustrative example. )

I'm working with a dataset that has multiple records (eg 'hotelStays') for each customer (custID). My goal is to get the number of days since a customer's previous stay as a new column in the data frame (ie each customer's first stay would have 'NA' as its value). To do so, I want to subtract each customer's previous checkOutDt from their current checkInDt. However, when I attempt to do so using lag(), all values in the new column are 'NA'.

Below is an example of the type of data with which I'm working.

custID	stayID	stayDt	checkInDt	checkOutDt
AAAAA	11111	01/15/1995	01/10/1995	01/17/1995
BBBBB	11112	02/08/1995	02/02/1995	02/25/1995
AAAAA	11113	03/01/1995	03/01/1995	03/03/1995
AAAAA	11114	06/24/1995	06/22/1995	07/02/1995
BBBBB	11115	10/02/1995	10/01/1995	10/10/1995
CCCCC	11116	01/08/1996	01/05/1996	01/17/1996
AAAAA	11117	05/15/1996	05/10/1996	05/28/1996

Ideally, the new column, 'daysSinceLastStay', would have the following values:

daysSinceLastStay
NA
NA
43
111
218
NA
313

However, I think I need to sort by custID and stayDt first.

---

Below is my current attempt at the code:

hotelData <- hotelData %>%
                arrange(custID, stayDt) %>%
                mutate(daysSinceLastStay = 
                       checkInDt - lag(checkOutDt))

---

Any advice is greatly appreciated!

Answer 1

Based on the data you're expecting, it seems like you're needing to make use of the group_by() function. This should get you what you're looking for.

# t*r*ibble, for creating data by row
hotelData <- tibble::tribble(
  ~custID, ~stayID, ~stayDt, ~checkInDt, ~checkOutDt,
  "AAAAA",  11111,  "01/15/1995",   "01/10/1995",   "01/17/1995",
  "BBBBB",  11112,  "02/08/1995",   "02/02/1995",   "02/25/1995",
  "AAAAA",  11113,  "03/01/1995",   "03/01/1995",   "03/03/1995",
  "AAAAA",  11114,  "06/24/1995",   "06/22/1995",   "07/02/1995",
  "BBBBB",  11115,  "10/02/1995",   "10/01/1995",   "10/10/1995",
  "CCCCC",  11116,  "01/08/1996",   "01/05/1996",   "01/17/1996",
  "AAAAA",  11117,  "05/15/1996",   "05/10/1996",   "05/28/1996"
)

# convert the date columns to the proper data type
# then, sort the data by customer ID and stayID
hotelData <- hotelData %>%
  mutate(across(stayDt:checkOutDt, lubridate::mdy)) %>%
  arrange(custID, stayID)

# within each customer, take the difference in days
hotelData %>%
  group_by(custID) %>%
  mutate(daysSinceLastStay = as.numeric(checkInDt - lag(checkOutDt)))

# A tibble: 7 x 6
# Groups:   custID [3]
  custID stayID stayDt     checkInDt  checkOutDt daysSinceLastStay
  <chr>   <dbl> <date>     <date>     <date>                 <dbl>
1 AAAAA   11111 1995-01-15 1995-01-10 1995-01-17                NA
2 AAAAA   11113 1995-03-01 1995-03-01 1995-03-03                43
3 AAAAA   11114 1995-06-24 1995-06-22 1995-07-02               111
4 AAAAA   11117 1996-05-15 1996-05-10 1996-05-28               313
5 BBBBB   11112 1995-02-08 1995-02-02 1995-02-25                NA
6 BBBBB   11115 1995-10-02 1995-10-01 1995-10-10               218
7 CCCCC   11116 1996-01-08 1996-01-05 1996-01-17                NA