Writing code for calculating Cmax and Tmax of Concentration_Time data - r

Question

I have a concentration-time data of many individuals. I want to find out the Cmax (maximum concentration) and Tmax (the time at Cmax) for each individual. I want to retain the results in R by adding a new "Cmax" and "Tmax" columns to the original dataset.
The data frame looks like this:
#df <-
ID TIME CONC
1 0 0
1 1 10
1 2 15
1 5 12
2 1 5
2 2 10
2 5 20
2 6 10
Ans so on. I started with something to find Cmax for an individual but its not getting me any where. Any help in fixing the code or an easier way of finding both (Cmax, and Tmax) is highly appreciable !
Cmax=function(df) {
n = length(df$CONC)
c_temp=0 # this is a temporary counter
c_max=0
for(i in 2:n){
if(df$CONC[i] > df$CONC[i-1]{
c_temp= c_temp+1
if(c_temp > c_max) c_max=c_temp # check
}
}
return(c_max)
}

Answer 1

Try
library(dplyr)
df %>%
group_by(ID) %>%
mutate(Cmax= max(CONC), Tmax=TIME[which.max(CONC)])
# ID TIME CONC Cmax Tmax
#1 1 0 0 15 2
#2 1 1 10 15 2
#3 1 2 15 15 2
#4 1 5 12 15 2
#5 2 1 5 20 5
#6 2 2 10 20 5
#7 2 5 20 20 5
#8 2 6 10 20 5
Or using data.table
library(data.table)
setDT(df)[, c("Cmax", "Tmax") := list(max(CONC),
TIME[which.max(CONC)]), by=ID]
Or using split from base R
unsplit(lapply(split(df, df$ID), function(x)
within(x, {Cmax <- max(CONC)
Tmax <- TIME[which.max(CONC)] })),
df$ID)
# ID TIME CONC Tmax Cmax
#1 1 0 0 2 15
#2 1 1 10 2 15
#3 1 2 15 2 15
#4 1 5 12 2 15
#5 2 1 5 5 20
#6 2 2 10 5 20
#7 2 5 20 5 20
#8 2 6 10 5 20
data
df <- structure(list(ID = c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L), TIME = c(0L,
1L, 2L, 5L, 1L, 2L, 5L, 6L), CONC = c(0L, 10L, 15L, 12L, 5L,
10L, 20L, 10L)), .Names = c("ID", "TIME", "CONC"), class = "data.frame",
row.names = c(NA, -8L))