How to select the row with the maximum value in each group
Here's a data.table
solution:
require(data.table) ## 1.9.2
group <- as.data.table(group)
If you want to keep all the entries corresponding to max values of pt
within each group:
group[group[, .I[pt == max(pt)], by=Subject]$V1]
# Subject pt Event
# 1: 1 5 2
# 2: 2 17 2
# 3: 3 5 2
If you'd like just the first max value of pt
:
group[group[, .I[which.max(pt)], by=Subject]$V1]
# Subject pt Event
# 1: 1 5 2
# 2: 2 17 2
# 3: 3 5 2
In this case, it doesn't make a difference, as there aren't multiple maximum values within any group in your data.
The most intuitive method is to use group_by and top_n function in dplyr
group %>% group_by(Subject) %>% top_n(1, pt)
The result you get is
Source: local data frame [3 x 3]
Groups: Subject [3]
Subject pt Event
(dbl) (dbl) (dbl)
1 1 5 2
2 2 17 2
3 3 5 2
A shorter solution using data.table
:
setDT(group)[, .SD[which.max(pt)], by=Subject]
# Subject pt Event
# 1: 1 5 2
# 2: 2 17 2
# 3: 3 5 2