[R] Matching where the source file has one record/ subject and the to-be-matched file has multiple records/subect

[Bert Gunter]

" I am not showing code, because I don't know how to write the code." (John
Sorkin)

Fortune!?

(not sure if this is legit, as it's about R-Help and not R).

Cheers,
Bert


On Wed, Jul 22, 2026 at 12:58 PM Sorkin, John <jsorkin using som.umaryland.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 file
> 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 will
> 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 problem!
>
> 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
>
>
>
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