drop columns that take less than n values?

Question

Suppose i have a data frame like the following:

df <- data.frame(v1 = sample(1:10, 100, replace = T), v2 = sample(LETTERS, 100, replace = T),
                         


        

Answer 1

Clunky but it works...

x<-as.data.frame(t(apply(df,2,function(x) length(x[unique(x)]))>10))

df[,names(x[,x>0])]

Answer 2

Alternatively, you can use select_if() from dplyr where you can pass a function as predicate to select columns:

library(dplyr)
df %>% select_if(function(col) n_distinct(col) > 10)

#    v2 V3 v4
#1    T  a 12
#2    R  k  7
#3    L  l  1
# ...