dplyr join with OR condition? - r

Question

I am wondering whether there is any way, preferably in the tidyverse, to join two dataframes based on OR conditions.
There are two dataframes: df_obs and df_event.
a) The join should happen if there is a match between
the obs_id and event_id; and obs_date or event_date, or both are NA.
OR
b) the obs_date and event_date are identical; and obs_id, event_id, or both are NA.
The match should not happen if obs_id is not identical to event_id (if both are not NA) OR
obs_date and event_date are not identical (both being not NA).
The result should look like df_res below. The column 'event' from the df_event is added to the df_obs.
I have seen the answer to this question, but maybe there is a way around SQL?
df_obs <- tibble::tribble(
~obs, ~obs_date, ~obs_id,
"a1", NA, 10L,
"a2", "01/01/2000", NA,
"b", "02/01/2000", NA,
"a3", "03/01/2000", 10L
)
df_obs
#> # A tibble: 4 × 3
#> obs obs_date obs_id
#> <chr> <chr> <int>
#> 1 a1 <NA> 10
#> 2 a2 01/01/2000 NA
#> 3 b 02/01/2000 NA
#> 4 a3 03/01/2000 10
df_event <- tibble::tribble(
~event, ~event_date, ~event_id,
"A", "01/01/2000", 10L,
"B", "02/01/2000", NA
)
df_event
#> # A tibble: 2 × 3
#> event event_date event_id
#> <chr> <chr> <int>
#> 1 A 01/01/2000 10
#> 2 B 02/01/2000 NA
df_res <- tibble::tribble(
~obs, ~obs_date, ~obs_id, ~event,
"a1", NA, 10L, "A",
"a2", "01/01/2000", NA, "A",
"b", "02/01/2000", NA, "B",
"a3", "03/01/2000", 10L, NA
)
df_res
#> # A tibble: 4 × 4
#> obs obs_date obs_id event
#> <chr> <chr> <int> <chr>
#> 1 a1 <NA> 10 A
#> 2 a2 01/01/2000 NA A
#> 3 b 02/01/2000 NA B
#> 4 a3 03/01/2000 10 <NA>
Created on 2022-09-13 with reprex v2.0.2

Answer 1

I can come up only with this solution:
df_obs %>%
left_join(df_event, by = c("obs_id" = "event_id"), na_matches='never') %>%
mutate(event = ifelse(!(is.na(obs_date)|is.na(event_date)|obs_date == event_date), NA, event)) %>%
select(-event_date) %>%
left_join(df_event, by = c("obs_date" = "event_date"), na_matches='never') %>%
mutate(event.y = ifelse(!(is.na(obs_id)|is.na(event_id)|obs_id == event_id), NA, event.y)) %>%
select(-event_id) %>%
mutate(event = ifelse(is.na(event.x), event.y, event.x)) %>%
select(-c(event.x, event.y))