[R] R Processing dataframe by group - equivalent to SAS by group processing with a first. and retain statments

[Tom Woolman]

Oh and don't forget:

#first line of code, bring dplyr into memory after that package has been installed.

library(dplyr)




On Wednesday, November 27th, 2024 at 12:05 PM, Tom Woolman <twoolman using ontargettek.com> wrote:

> 
> 
> Check out the dplyr package, specifically the mutate function.
> 
> # Create new column based on existing column value
> 
> df <- df %>% mutate(FirstDay = if(ID = 2, 5))
> 
> 
> df
> 
> 
> 
> Repeat as needed to capture all of the day/firstday combinations you want to account for.
> 
> Like everything else in R, there are probably at least a dozen other ways to do this, between base R and all of the library packages available.
> 
> 
> 
> 
> On Wednesday, November 27th, 2024 at 11:30 AM, Sorkin, John jsorkin using som.umaryland.edu wrote:
> 
> > I am an old, long time SAS programmer. I need to produce R code that processes a dataframe in a manner that is equivalent to that produced by using a by statement in SAS and an if first.day statement and a retain statement:
> > 
> > I want to take data (olddata) that looks like this
> > ID Day
> > 1 1
> > 1 1
> > 1 2
> > 1 2
> > 1 3
> > 1 3
> > 1 4
> > 1 4
> > 1 5
> > 1 5
> > 2 5
> > 2 5
> > 2 5
> > 2 6
> > 2 6
> > 2 6
> > 3 10
> > 3 10
> > 
> > and make it look like this:
> > (withing each ID I am copying the first value of Day into a new variable, FirstDay, and propagating the FirstDay value through all rows that have the same ID:
> > 
> > ID Day FirstDay
> > 1 1 1
> > 1 1 1
> > 1 2 1
> > 1 2 1
> > 1 3 1
> > 1 3 1
> > 1 4 1
> > 1 4 1
> > 1 5 1
> > 1 5 1
> > 2 5 5
> > 2 5 5
> > 2 5 5
> > 2 6 5
> > 2 6 5
> > 2 6 5
> > 3 10 3
> > 3 10 3
> > 
> > SAS code that can do this is:
> > 
> > proc sort data=olddata;
> > by ID Day;
> > run;
> > 
> > data newdata;
> > retain FirstDay;
> > set olddata;
> > by ID;
> > if first.ID then FirstDay=Day;
> > run;
> > 
> > I have NO idea how to do this is R (so I can't post test-code), but below I have R code that creates olddata:
> > 
> > ID <- c(rep(1,10),rep(2,6),rep(3,2))
> > date <- c(rep(1,2),rep(2,2),rep(3,2),rep(4,2),rep(5,2),
> > rep(5,3),rep(6,3),rep(10,2))
> > date
> > olddata <- data.frame(ID=ID,date=date)
> > olddata
> > 
> > Any suggestions on how to do this would be appreciated. . . I have worked on this for more than 12-hours, despite multiple we searches I have gotten nowhere. . .
> > 
> > Thanks
> > 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
> > 
> > ______________________________________________
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> > 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 using 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.