[R] Matching when each subject has multiple records, but each subject should be used only once in the match

[Sorkin, John]

I have a file that contains longitudinal data for each subject. As a result, each subject can have multiple records. For example a given subject might have a record in Jan 2020, another in June 2020, another in Feb 2021, another in May 2021, another in Sept 2022, etc. At each time for which a subject has a record the subject is identified as a case or a control.

Over the course of the longitudinal data, I want to match a given case to a given control. Once a subject is matched, I don't want the subject to be eligible for being matched again.

If each subject had a single record, matching could easily be accomplished. How can I accomplish the match in my file having repeated measures for each subject?

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; 
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 and Paliative Care,
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
Cell phone 443-418-5382