R / lubridate: Calculate number of overlapping days between two periods

Question

I am trying to calculate the number of overlapping days between two time periods. One period is fixed in a start and end date, the other is recorded as start and end dates i

Answer 1

We can use pmin/pmax to get the min/max of two sets of vectors

df %>% 
   mutate(overlap = ifelse(my.start > end, 0, pmin(my.end, end) - 
                                 pmax(my.start, start) + 1))
#       start        end overlap
#1 2018-07-15 2018-07-20   0
#2 2018-07-20 2018-08-05   5
#3 2018-08-15 2018-08-19   5
#4 2018-08-20 2018-09-15  12
#5 2018-09-01 2018-09-15   0

---

If we want to use the same option as in the OP's code, i.e. min/max, either with rowwise() or using map2, we loop through rows

library(purrr)
df %>% 
  mutate(overlap = map2_dbl(start, end, ~
        max( as.integer(min(my.end, .y) - max(my.start, .x) + 1), 0)))

Noticed that the OP's actual data have time component. In that case, change the above solution by converting to Date class

df %>% 
   mutate(overlap = map2_dbl(start, end, ~
     max(as.integer(min(my.end, as.Date(.y)) - max(my.start, as.Date(.x)) + 1), 0)))