[R] Data extraction and assembly from a data frame

[arun]

You could try:
library(plyr)
res <- ddply(TestData[,-2],.(ID),numcolwise(max)) 
colnames(res)[-1] <- paste0(colnames(res)[-1],".max")
A.K.




On Friday, June 20, 2014 3:43 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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