Re: Matching where the source file has one record/ subject and the to-be-matched file has multiple records/subect

If you have not found any of the responses (including Ravi's) sufficiently
helpful, I would suggest that you provide a reprex (which does *not*
require code for a solution).

Issues that seemed to me to require further clarification are:

1. After a subject's date in file 1 is matched to a date in file 2 and all
the records in file 2 for the matched subject of that date removed, do you
continue to seek matches for that file 1 date and remove further subjects
from file 2, or do you go on to the next record in file 1?

2. Can there be many identical dates in file 1 (this is related to point 1)
above)? Same question for file 2?

Apologies if this is just my stupidity and these points are obvious or
irrelevant.

Cheers,
Bert

On Wed, Jul 22, 2026 at 12:58=E2=80=AFPM Sorkin, John <[email protected]=
d.edu>
wrote:

> I am not showing code, because I don't know how to write the code. I know
> that MatchIt performs propensity score matching, but I don't know how to
> use the function to perform the match I want to conduct.
>
> I have two files
> File 1: a list of n  records, 1 record/subject. Each record has a subject
> number and a date
> File 2: a list of m records m>>n with multiple records/subject but each
> record has a distinct date. All records for a given subject in file 2 have
> the same subject number, but each record has a different date.
>
> I want to match each record from file 1 with a single record from file 2
> based on date. Once a record from file 2 is matched with a record from fi=
le
> 1, I want to remove all records from file 2 for the subject who was used =
in
> the match with the subject from file 1 so that the subject from file 2 wi=
ll
> not be used in any future match.
>
>
> Example
> file 1                                          file 2
> subject   date                              subject   date
> 1              01/01/2020                  100   01/01/2020
> 2              01/01/2021                  100   01/10/2021
> 3                                                   101  02/01/2021
>
> Subject 1 from file 1 is a perfect match for subject 100 from file2. The
> subjects are matched.
> All data from file 2 is removed for subject 100.
> Subject 2 from file 1 is then matched with subject 101 from file 2.
> If all records from subject 100 had not been removed from file2, subject 2
> would have been matched to subject 100 date 01/10/2021. I don't want this
> to happen. Once subject 100 is used to match subject 1, I don't want any
> other person from file 1 to be matched with subject 100.
>
> I hope you can help me with this, I suspect, not uncommon matching proble=
m!
>
> Thank you,
> John
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine, University of Maryland School of Medicine;
> Associate Director for Biostatistics and Informatics, Baltimore VA Medical
> Center Geriatrics Research, Education, and Clinical Center;
> Former PI Biostatistics and Informatics Core, University of Maryland
> School of Medicine Claude D. Pepper Older Americans Independence Center;
> Senior Statistician University of Maryland Center for Vascular Research;
>
> Division of Gerontology, Geriatrics and Palliative Medicine,
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> Cell phone 443-418-5382
>
>
>
> ______________________________________________
> [email protected] mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

	[[alternative HTML version deleted]]