How to select the row with the maximum value in ea

Question

Currently I have a problem as follows. In a dataset where multiple observations for each subject exist, and I want to make a subset of this dataset where only the maximum data for a record is selected. For example, for a data set as below:

ID <- c(1,1,1,2,2,2,2,3,3)
Value <- c(2,3,5,2,5,8,17,3,5)
Event <- c(1,1,2,1,2,1,2,2,2)

group <- data.frame(Subject=ID, pt=Value, Event=Event)

Subject 1, 2 and 3 have the biggest pt value of 5, 17 and 5 respectively. How could I first, find the biggest pt value for each subject, and then, put this observation in another data frame? This means that this subset would only have the biggest pt values for each subject.

Answer 1

Another option is slice

library(dplyr)
group %>%
     group_by(Subject) %>%
     slice(which.max(pt))
#    Subject    pt Event
#    <dbl> <dbl> <dbl>
#1       1     5     2
#2       2    17     2
#3       3     5     2

Answer 2

I wasn't sure what you wanted to do about the Event column, but if you want to keep that as well, how about

isIDmax <- with(dd, ave(Value, ID, FUN=function(x) seq_along(x)==which.max(x)))==1
group[isIDmax, ]

#   ID Value Event
# 3  1     5     2
# 7  2    17     2
# 9  3     5     2

Here we use ave to look at the "Value" column for each "ID". Then we determine which value is the maximal and then turn that into a logical vector we can use to subset the original data.frame.