select maximum row value by group

Question

I\'ve been trying to do this with my data by looking at other posts, but I keep getting an error. My data new looks like this:

id  year    name          


        

Answer 1

Your ddply effort looks good to me, but you referenced the original dataset in the callback function.

ddply(new,~id,function(x){x[which.max(new$year),]})
# should be
ddply(new,.(id),function(x){x[which.max(x$year),]})