Matching when each subject has multiple records

?
mydf <- data.frame(date = as.Date("2010-01-01") + sample(500, size = 20), subject = sample(c("A", "B", "C"), 20, replace = TRUE), first = FALSE)
mydf <- mydf[order(mydf$date),]
df_split <- split(mydf, f = mydf$subject)
df_split <- lapply(df_split, function(df) {df[1, "first"] <- TRUE; df})
mydf <- do.call(rbind, df_split)

Naresh,

I appreciate your reply.

In my original posting, I neglected to mention that I want to propensity score match the two groups. I don't think you suggestion will help me propensity score match my data. Am I missing something?

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;
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
?

> mydf <- data.frame(date = as.Date("2010-01-01") + sample(500, size = 20), subject = sample(c("A", "B", "C"), 20, replace = TRUE), first = FALSE)
> mydf <- mydf[order(mydf$date),]
> df_split <- split(mydf, f = mydf$subject)
> df_split <- lapply(df_split, function(df) {df[1, "first"] <- TRUE; df})
> mydf <- do.call(rbind, df_split)

        [[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org 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.
I don't think you will get a useful response without providing a subset of
your data with detailed information on what variables are the subject
specific covariates to be used for propensity score matching, what your
response(s) is/are, how you intend to model the responses (e.g. survival
time or death, or whatever it is), whether there are time specific
covariates, etc.

It is not even clear to me whether propensity score matching is
useful/appropriate -- but what do I know?!

It is also not clear to me that this is an R programing issue or a
statistical issue and therefore not really on topic for this list.

Obviously, feel free to ignore any/all of the above.

Cheers,
Bert

On Thu, Sep 18, 2025 at 8:03?AM Sorkin, John <jsorkin at som.umaryland.edu>
wrote:
Naresh,

I appreciate your reply.

In my original posting, I neglected to mention that I want to propensity
score match the two groups. I don't think you suggestion will help me
propensity score match my data. Am I missing something?

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;
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

________________________________________
From: R-help <r-help-bounces at r-project.org> on behalf of Naresh Gurbuxani
<naresh_gurbuxani at hotmail.com>
Sent: Thursday, September 18, 2025 10:10 AM
To: r-help at r-project.org <r-help at r-project.org>
Subject: [R] Fwd: Matching when each subject has multiple records

?

mydf <- data.frame(date = as.Date("2010-01-01") + sample(500, size =
20), subject = sample(c("A", "B", "C"), 20, replace = TRUE), first = FALSE)
mydf <- mydf[order(mydf$date),]
df_split <- split(mydf, f = mydf$subject)
df_split <- lapply(df_split, function(df) {df[1, "first"] <- TRUE; df})
mydf <- do.call(rbind, df_split)

        [[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org 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.

______________________________________________
R-help at r-project.org 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.