How to aggregate data in R with mode (most common) value for each row?

Question

I have a data set for example,

Data <- data.frame(
  groupname = as.factor(sample(c(\"a\", \"b\", \"c\"), 10, replace = TRUE)),
  someuser = sample(c(\"x\         


        

Answer 1

Many options. Here one using table to compute frequency and which.max to select max occurred. within data.table framework:

library(data.table)
setDT(Data)[,list(someuser={
  tt <- table(someuser)
  names(tt)[which.max(tt)]
}),groupname]

using plyr( nearly the same) :

library(plyr)
ddply(Data,.(groupname),summarize,someuser={
  tt <- table(someuser)
  names(tt)[which.max(tt)]
})