Conditional statement within loop using multiple datasets R - r

Question

I would like to figure out who was the most recent previous owner at a location within the last two years before the current owner. The locations are called reflo (reference location). Note that there is not always an exact match for reflo.x and reflo within two years (so a solution that allows me to add additional conditions, such as to find the next closest reflo, would be extra helpful).
The conditions:
the previous owner has to have lived at the same location (lifetime_census$reflo==owners$reflo.x[i]) within two years of the current owner's year (lifetime_census$census_year <= 2 years of owners$spr_census)
if none, then assign NA
Previous owners (>20,000) are stored in a dataset called lifetime_census. Here is a sample of the data:
id previous_id reflo census_year
16161 5587 -310 2001
17723 5587 -310 2002
19345 5879 -310 2003
16848 5101 Q1 2001
17836 6501 Q1 2002
19439 6501 Q1 2003
21815 6057 Q1 2004
I then have an owners dataset (here is a sample):
squirrel_id spr_census reflo.x
6391 2005 Q1
6130 2005 -310
6288 2005 A12
To illustrate what I am trying to achieve:
squirrel_id spr_census reflo.x previous_owner census_year
6391 2005 Q1 6057 2004
6130 2005 -310 5879 2003
6288 2005 A12 NA NA
What I have currently tried is this:
n <- length(owners$squirrel_id)
for(i in 1:n) {
last_owner <- subset(lifetime_census,
life_census$previous_id!=owners$squirrel_id[i] & #previous owner != current owner
lifetime_census$reflo==owners$reflo.x[i] &
lifetime_census$census_year<=owners$spr_census[i]) #owners can be in current or past year
#Put it all together
owners[i,"spring_owner"] <- last_owner$previous_id[i]
}
This gives me a new column for the previous owner in any past year for reflo.x, adding NAs after all the conditions are not met. I cannot figure out how to restrict this search to the last two years.
Any ideas? (Note that there is not always an exact match for reflo.x and reflo within two years (so a solution that allows me to add additional conditions, such as to find the next closest reflo, would be extra helpful).)

Answer 1

To figure out who was the most recent previous owner at a location within the last two years before the current owner you can first arrange by date in descending order:
library(dplyr)
lifetime_census<-lifetime_census %>%
group_by(reflo) %>%
arrange(desc(census_date))
Which puts the most recent years first (similar to top_n):
id previous_owner reflo census_year
19345 5879 -310 2003
17723 5587 -310 2002
16161 5587 -310 2001
21815 6057 Q1 2004
19439 6501 Q1 2003
17836 6501 Q1 2002
16848 5101 Q1 2001
Then you can run the loop above:
n <- length(owners$squirrel_id)
for(i in 1:n) {
last_owner <- subset(lifetime_census,
life_census$squirrel_id != owners$squirrel_id[i] &
lifetime_census$reflo==owners$reflo.x[i] &
lifetime_census$census_year <= owners$spr_census[i]) #owners can be in current or past year
#Put it all together
owners[i,"previous_owner"] <- last_owner$previous_owner[i]
owners[i,"prev_census"] <- last_owner$census_year[i]
}
This will give you:
> head(owners)
> squirrel_id spr_census reflo.x previous_owner prev_census
<chr> <chr> <chr> <chr> <dbl>
6391 2005 Q1 6057 2004
6130 2005 -310 5879 2003
6288 2005 A12 <NA> <NA>
If, for example, an individual above had a match for a year <= 2 years from the spr_census year, you can fix this on a case by case basis (not the most elegant solution, but it's workable) by using an if_else statement, like so:
owners<-owners%>% mutate(spring_owner=ifelse(prev_census < 2003, "<NA>", spring_owner))