Selecting Max Column Values in R

Question

I\'m pretty new to R and have a question regarding selecting the max values in a column.

I have the following data frame:

          X      Y
 [1,]            


        

Answer 1

You can use ave with a custom function that wraps max, so you can remove NA values:

Data$Y <- ave(Data$Y, Data$X, FUN=function(x) max(x, na.rm=TRUE))

Answer 2

With the dplyr or data.table packages, you get an easy way group to calculate grouped operations.

dplyr solution

require(dplyr)
Data %>% group_by(X) %>% mutate(Y = max(Y, na.rm=TRUE))

data.table solution

require(data.table)
setDT(Data)[, Y:=max(Y, na.rm=TRUE), by=X][]