Dear list members,
I am trying to create a subset of a data frame based on conditions in two
columns, and after spending much time trying (and search R-help) have not had
any luck. Essentially, I have a data frame that is something like this:
date<-as.POSIXct(as.character(c("2012-01-25","2012-01-25","2012-01-26","2012-01-27","2012-01-27","2012-01-27")))
time<-as.POSIXct(as.character(c("13:20", "13:40", "14:00", "10:00", "10:20",
"10:20")), format="%H:%M")
count<-c(12,14,11,12,12,8)
data<-data.frame(date,time,count)
which looks like:
date time count
1 2012-01-25 13:20:00 12
2 2012-01-25 13:40:00 14
3 2012-01-26 14:00:00 11
4 2012-01-27 10:00:00 12
5 2012-01-27 10:20:00 12
6 2012-01-27 10:20:00 8
I would like to create a subset by doing the following: for each unique date,
only include one case which will be the case with the max value for the column
labelled "count". So the resulting subset would be:
date time count
2 2012-01-25 13:40:00 14
3 2012-01-26 14:00:00 11
4 2012-01-27 10:00:00 12
Some dates have two cases at which the "count" was the same, but I only want to
include one case (I don't really mind which case it chooses, but if need be it
could be based on the earliest "time" for which the same counts occurred). I
have tried various loops with no success! I'm sure that there is an easy answer
that I have not found! Any help is much appreciated!!
All the best,
Chandra
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