list all factor levels of a data.frame
Solution 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(.))))
Solution 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)
Solution 3
Or using purrr:
data %>% purrr::map(levels)
Or to first factorize everything:
data %>% dplyr::mutate_all(as.factor) %>% purrr::map(levels)
And answering the question about how to get the lengths:
data %>% map(levels) %>% map(length)
Solution 4
A simpler method is to use the sqldf package and use a select distinct statement. This makes it easier to automatically get the names of factor levels and then specify as levels to other columns/variables.
Generic code snippet is:
library(sqldf)
array_name = sqldf("select DISTINCT *colname1* as '*column_title*' from *table_name*")
Sample code using iris dataset:
df1 = iris
factor1 <- sqldf("select distinct Species as 'flower_type' from df1")
factor1 ## to print the names of factors
Output:
flower_type
1 setosa
2 versicolor
3 virginica
Solution 5
In case you want to display factor levels only for thos columns which are declared as.factor
, you can use:
lapply(df[sapply(df, is.factor)], levels)
ckluss
Updated on April 01, 2021Comments
-
ckluss about 3 years
with
str(data)
I get thehead
of 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 forlevels(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
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BigDataScientist about 8 yearsHow do we get length of all of those levels
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G. Grothendieck almost 8 yearsIf you indent each code line by 4 spaces it will format itself properly.
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Amit Kohli over 6 years@BigDataScientist check my answer
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igorkf over 4 yearsNice approach. I like it.