Hi,
is there a specific reason to use "shift"? I mean, you could easily
achieve what you described by simple indexing:
--- snjp ---
for (i in 1:10) {
cat("x[i,num]",x[i,"num"],"\n")
# Get previous value of x[i,"num"]
zoop<-x[i-1,"num"] # NB! Returns "integer(0)" for row index 0
cat("Previous value of x[,num]=",zoop,"\n")
}
--- snip ---
The code above just loops through the *rows* from 1 to 10 and dumps the
"num" value from the previous row. If you want to get the "num" value
from the row above a specific "Id", then the zoop-line should look
something like this:
zoop<-x[which(x["Id"]==i)-1, "num"]
HTH,
Kimmo
Sorkin, John kirjoitti 29.11.2024 klo 3.25:
> I need to write code that will give me the previous value of from a
> data.frame. I have written the following code using the shift function from
> data.table . It does not work. I hope someone can help me correct the code.
> ###########################
> # Try to understand shift #
> ###########################
> if(!require(data.table)) install.packages("data.table")
> library(data.table)
> # Create data
> x <- data.frame(Id=rep(1:10),num=rep(11:20))
> cat("This is the input data.frame used in the code below","\n")
> x
>
> for (i in 1:10) {
> cat("x[i,num]",x[i,"num"],"\n")
> # Get previous value of x[i,"num"]
> zoop<-shift(x[i,"num"], n=1L, type="lag")
> cat("Previous value of x[,num]=",zoop,"\n")
> }
> ###############################
> # END Try to understand shift #
> ###############################
>
> 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
>
>
>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> and provide commented, minimal, self-contained, reproducible code.
--
Kimmo Elo
Senior Lecturer | Adjunct professor, Dr.
========================================================
University of Eastern Finland
Department of Geographical and Historical Studies
P.O. Box 111
FIN-80101 Joensuu
Finland
E-mail: kimmo....@uef.fi
ResearchGate: http://www.researchgate.net/profile/Kimmo_Elo
LAWPOL Consortium (PI): https://lawpol.fi/en
========================================================
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R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
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