aggregate - Rename factor levels based on a condition in R -

i want combine factors count less n 1 factor named "else"

for example if n = 3 in following df want combine "c", "d" , "e" "else":

df = data.frame(x=c(1:10), y=c("a","a","a","b","b","b","c","d","d","e")) 

i started out getting df low count values:

library(plyr) lowcounts = ddply(df, "y", function(z){if(nrow(z)<3) nrow(z) else null}) 

i know change these manually in practice have dozens of levels need automate this.

i want select , rename levels %in% lowcount in levels(df) , leave rest same not sure how proceed.

another alternative:

#your dataframe df = data.frame(x=c(1:10), y=c("a","a","a","b","b","b","c","d","d","e"))  #which levels keep , change res <- table(df$y) notkeep <- names(res[res < 3]) keep <- names(res)[!names(res) %in% notkeep] names(keep) <- keep  #set new levels levels(df$y) <- c(keep, list("else" = notkeep))  df #    x    y #1   1    #2   2    #3   3    #4   4    b #5   5    b #6   6    b #7   7 else #8   8 else #9   9 else #10 10 else