list all factor levels of a data.frame

Question

with str(data) I get the headof the levels (1-2 values)

fac1: Factor w/ 2  levels ... : fac2: Factor w/ 5  levels ... : fac3: Factor w/ 20 levels ... : val: num ... 

with dplyr::glimpse(data) I get more values, but no infos about number/values of factor-levels. Is there an automatic way to get all level informations of all factor vars in a data.frame? A short form with more info for

levels(data$fac1) levels(data$fac2) levels(data$fac3) 

or more precisely a elegant version for something like

for (n in names(data))   if (is.factor(data[[n]])) {     print(n)     print(levels(data[[n]]))   } 

thx Christof

Answer 1

Here are some options. We loop through the 'data' with sapply and get the levels of each column (assuming that all the columns are factor class)

sapply(data, levels) 

Or if we need to pipe (%>%) it, this can be done as

library(dplyr) data %>%       sapply(levels) 

Or another option is summarise_each from dplyr where we specify the levels within the funs.

 data %>%       summarise_each(funs(list(levels(.)))) 

Answer 2

If your problem is specifically to output a list of all levels for a factor, then I have found a simple solution using :

unique(df$x)

For instance, for the infamous iris dataset:

unique(iris$Species)