Matching data from unequal length data frames in r

Question

This seems like it should be really simple. Ive 2 data frames of unequal length in R. one is simply a random subset of the larger data set. Therefore, they have the same exact data and a UniqueID that is exactly the same. What I would like to do is put an indicator say a 0 or 1 in the larger data set that says this row is in the smaller data set.

I can use which(long$UniqID %in% short$UniqID) but I can't seem to figure out how to match this indicator back to the long data set

Answer 1

Made same sample data.

long<-data.frame(UniqID=sample(letters[1:20],20))
short<-data.frame(UniqID=sample(letters[1:20],10))

You can use %in% without which() to get values TRUE and FALSE and then with as.numeric() convert them to 0 and 1.

long$sh<-as.numeric(long$UniqID %in% short$UniqID)