R calculate overlapping months between two start and end dates - r

Question

I have a dataframe with two start and stop dates that looks like this:
ID G1_START G1_END G2_START G2_END LOCATION
1 1/1/2021 5/31/2021 2/1/2021 5/31/2021 A
2 12/1/2020 3/31/2021 10/1/2020 5/31/2021 B
What I would like to do is create one row per month per patient where the months overlap between the four dates. For example
ID MONTH ACTIVE LOCATION
1 2/1/2021 1 A
1 3/1/2021 1 A
1 4/1/2021 1 A
1 5/1/2021 1 A
2 12/1/2020 1 B
2 1/1/2021 1 B
2 2/1/2021 1 B
2 3/1/2021 1 B
Where active means the ID was on both G1 and G2 during these months.

Answer 1

Here is a method in tidyverse
Reshape data from wide to long format - pivot_longer
Convert the date columns 'START', 'END' to Date class (mdy)
Loop over the 'START', 'END' with map2, get the sequence by '1 month'
Floor the date by month - floor_date
grouped by ID, LOCATION, MONTH, filter the groups where 'Categ' distinct elements are 2
Create 'ACTIVE' column of 1 after returning the distinct rows
library(dplyr)
library(tidyr)
library(lubridate)
library(purrr)
pivot_longer(df1, cols = contains("_"),
names_to = c("Categ", ".value"), names_sep= "_") %>%
transmute(ID, LOCATION, Categ, MONTH = map2(mdy(START), mdy(END), ~
floor_date(seq(.x, .y, by = '1 month'), 'month'))) %>%
unnest(MONTH) %>%
group_by(ID, LOCATION, MONTH) %>%
filter(n_distinct(Categ) == 2) %>%
ungroup %>%
distinct(ID, LOCATION, MONTH) %>%
mutate(ACTIVE = 1) %>%
select(ID, MONTH, ACTIVE, LOCATION)
-output
# A tibble: 8 x 4
ID MONTH ACTIVE LOCATION
<int> <date> <dbl> <chr>
1 1 2021-02-01 1 A
2 1 2021-03-01 1 A
3 1 2021-04-01 1 A
4 1 2021-05-01 1 A
5 2 2020-12-01 1 B
6 2 2021-01-01 1 B
7 2 2021-02-01 1 B
8 2 2021-03-01 1 B
data
df1 <- structure(list(ID = 1:2, G1_START = c("1/1/2021", "12/1/2020"
), G1_END = c("5/31/2021", "3/31/2021"), G2_START = c("2/1/2021",
"10/1/2020"), G2_END = c("5/31/2021", "5/31/2021"), LOCATION = c("A",
"B")), class = "data.frame", row.names = c(NA, -2L))