[R] Data extraction and assembly from a data frame

[William Dunlap]

Have you looked at the 'aggregate' function?  E.g.,
  aggregate(TestData[c("VAR1","VAR2","VAR3")], by=TestData["ID"], max)
Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Fri, Jun 20, 2014 at 12:42 PM, Jun Shen <jun.shen.ut at gmail.com> wrote:
> Hi all,
>
> Here is my situation. I have a dataframe, the structure would be something
> like this,
>
> TestData<-data.frame(ID=rep(1:10,each=10),TIME=rep(seq(0.1,1,0.1),10),VAR1=rnorm(100),VAR2=5*rnorm(100),VAR3=10*rnorm(100))
>
> Basically, I want to extract the maximum value from each ID for VAR1, VAR2,
> VAR3......
>
> The way I can think of is
>
> do.call(rbind,lapply(split(TestData,TestData$ID),function(x)x[which.max(x$VAR1),'VAR1']))
>
> and do this for each of the variables and put the results back. It's kind
> of clumsy but OK for several variables. I have dozens of them. Is there a
> better way to do it?
>
> It would be ideal to produce the results like
>
>    ID VAR1.max VAR2.max VAR3.max  1 1.2828796 8.63276 15.051992  2 1.1870067
> 8.691801 10.736301  3 1.2815352 6.335692 5.827524  4 1.6719411 5.998597
> 16.646212  5 1.5631107 6.067457 15.331046  6 0.718989 6.610279 7.306005  7
> 0.8734315 13.39844 16.965365  8 2.7447862 10.21613 22.545131  9 3.490395
> 10.83543 25.744662  10 0.4719087 11.73021 7.226687
> Thanks for any help.
>
> Jun Shen
>
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>
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