How to make a unique in R by column A and keep the row with maximum value in column B

Question

I have a data.frame with several columns (17). Column 2 have several rows with the same value, I want to keep only one of those rows, specifically the one that has the maxim

Answer 1

A solution using package data.table:

set.seed(42)
dat <- data.frame(A=c('a','a','a','b','b'),B=c(1,2,3,5,200),C=rnorm(5))
library(data.table)

dat <- as.data.table(dat)
dat[,.SD[which.max(B)],by=A]

   A   B         C
1: a   3 0.3631284
2: b 200 0.4042683