I'm still a novice at R, so this may be a bit convoluted but it works:
colnames(x) = c("date", "id", "value")
do.call(rbind, (dlply(as.data.frame(x), .(id), function (y)
y[-c(which(as.Date(y$date, "%m/%d/%y") == min(as.Date(y$date,
"%m/%d/%y")), arr.ind=T)),])))
- FA
------ Original Message ------
From: "Andras Farkas" <motyoc...@yahoo.com>
To: "r-help@r-project.org" <r-help@r-project.org>
Sent: 7/30/2013 8:13:21 AM
Subject: [R] selection based on dates
Dear All
please provide your insigths on the following:
I have:
a <-c("1/1/13",15,20)
b <-c("1/5/13",15,25)
c <-c("1/9/13",15,28)
d <-c("2/1/13",18,30)
e <-c("2/5/13",18,35)
f <-c("2/9/13",18,38)
x <-matrix(c(a,b,c,d,e,f),ncol=3,byrow=TRUE)
What I would like to do is to eliminate certain rows of this matrix
based on the date column values. As you can see, in the second column
my values (15 and 18) repeat 3 times each, so this column serves as an
ID number if you will. Thus each ID numbers show up with 3 different
date values in the first column. Now I would like to eliminate the rows
with the earliest date per ID number. My result should look like this:
z <-x[-c(1,4),]
as allways, your help is greatly appreciated,
thanks,
Andras
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
