Rename factor levels based on a condition in R

Question

I want to combine all factors with a count less than n into one factor named \"Else\"

For example if n = 3 then in the following df I want to combine \"c\", \"d\" and \"

Answer 1

Why not something like this?

library(data.table)
dt <- data.table(df)
dt[,ynew := ifelse(.N < 3, "else",as.character(y)), by = "y"]