How to create a dataset of ids that get treated at some point in time? (R) [duplicate]

Question

I have a longitudinal dataset with 3 important variables: ID, Year, Treatment

I would like to keep all the IDs that get treated at some point of time and drop all the IDs that never get treated. How do I do this on R?

Example:

ID	Year	Treatment
0001	2000	0
0001	2001	0
0001	2002	0
0002	2000	0
0002	2001	0
0002	2002	1

I would like to keep all observations of ID 0002 (Treated at some point in time), but drop all of ID 0001 (Never treated). I have a very big dataset with more IDs than that so I can not do this manually.

Thanks in advance.

Answer 1

Find the IDs that have treatment, then subset those IDs:

d[ d$ID %in% unique(d[ d$Treatment == 1,  "ID" ]), ]
#     ID Year Treatment
# 4 0002 2000         0
# 5 0002 2001         0
# 6 0002 2002         1