How to select the row with the maximum value in each group

Question

In a dataset with multiple observations for each subject I want to take a subset with only the maximum data value for each record. For example, with a following dataset:

Answer 1

do.call(rbind, lapply(split(group,as.factor(group$Subject)), function(x) {return(x[which.max(x$pt),])}))

Using Base R