[R] Data extraction and assembly from a data frame

[MacQueen, Don]

How about

aggregate(TestData[,c('VAR1','VAR2','VAR3')], by=list(id=TestData$ID),
FUN=max)




-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 6/20/14 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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