删除具有每个级别少于 5 个观测值的因子的列

Question

I have a dataset composed of more than 100 columns and all columns are of type factor. Ex:

          animal               fruit               vehicle              color 
             cat              orange                   car               blue 
             dog               apple                   bus              green 
             dog               apple                   car              green 
             dog              orange                   bus              green

In my dataset i need to remove all columns with factors thas has less than 5 observations per level. In this example, if i want to remove all columns with amount of observations per levels less than or equal to 1 , like blue or cat , the algorithm will remove the columns animal and color . What is the most elegant way to do this?

Answer 1

We can use Filter with table

Filter(function(x) !any(table(x) < 2), df1)
#  fruit vehicle
#1 orange     car
#2  apple     bus
#3  apple     car
#4 orange     bus

data

df1 <- structure(list(animal = structure(c(1L, 2L, 2L, 2L), .Label = c("cat", 
"dog"), class = "factor"), fruit = structure(c(2L, 1L, 1L, 2L
), .Label = c("apple", "orange"), class = "factor"), vehicle = structure(c(2L, 
1L, 2L, 1L), .Label = c("bus", "car"), class = "factor"), color = structure(c(1L, 
2L, 2L, 2L), .Label = c("blue", "green"), class = "factor")),
row.names = c(NA, 
-4L), class = "data.frame")

Answer 2

We can use select_if from dplyr

library(dplyr)
df1 %>% select_if(~all(table(.) > 1))

#   fruit vehicle
#1 orange     car
#2  apple     bus
#3  apple     car
#4 orange     bus