Dropping factors which levels have observations smaller than a specific value-R

Question

Let I have such data frame(df1) with factors:

factor1  factor2  factor3
-------  -------  -------
d        a         x
d        a         x
b        a                


        

Answer 1

is that what you want?

df <- data.frame(col1=rep(letters[1:4], each=3),
                 col2=rep(letters[1:2], each=6),
                 col3=rep(letters[1:3], each=4))

ddf[, sapply(df, function(x) min(nlevels(x)) > 2)]