[R] Select rows based on matching conditions and logical operators

[arun]

Hi,

Try this:

dat1<-read.table(text="
PGID    PTID    Year    Visit  Count
6755    53121    2009    1    0
6755    53121    2009    2    0
6755    53121    2009    3    0
6755    53122    2008    1    0
6755    53122    2008    2    0
6755    53122    2008    3    1
6755    53122    2009    1    0
6755    53122    2009    2    1
6755    53122    2009    3    2
",sep="",header=TRUE)


dat2<-lapply(split(dat1,dat1$Count),function(x) x[which.max(x$Count),])
 do.call(rbind,dat2)
  PGID  PTID Year Visit Count
0 6755 53121 2009     1     0
1 6755 53122 2008     3     1
2 6755 53122 2009     3     2

A.K.



----- Original Message -----
From: kborgmann <borgmann at email.arizona.edu>
To: r-help at r-project.org
Cc: 
Sent: Wednesday, July 25, 2012 1:10 PM
Subject: [R] Select rows based on matching conditions and logical operators

Hi,
I have a dataset in which I would like to select rows based on matching
conditions and return the maximum value of a variable else return one row if
duplicate counts exist.  My dataset looks like this:
PGID    PTID    Year     Visit  Count
6755    53121    2009    1    0
6755    53121    2009    2    0
6755    53121    2009    3    0
6755    53122    2008    1    0
6755    53122    2008    2    0
6755    53122    2008    3    1
6755    53122    2009    1    0
6755    53122    2009    2    1
6755    53122    2009    3    2

I would like to select rows if PTID and Year match and return the maximum
count else return one row if counts are the same, such that I get this
output 
PGID    PTID    Year     Visit  Count
6755    53121    2009    1    0
6755    53122    2008    3    1
6755    53122    2009    3    2

I tried the following code and the output is almost correct but duplicate
values were included
df2<-with(df, sapply(split(df, list(PTID, Year)),
function(x) if (nrow(x)) x[which(x$Count==max(x$Count)),]))
df<-do.call(rbind,df)
rownames(df)<-1:nrow(df)

Any suggestions? 
Thanks much for your responses!




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