Factor levels
When you first get a dataset, you will often notice that it contains factors with specific factor levels. However, sometimes you will want to change the names of these levels for clarity or other reasons. R allows you to do this with the function levels():
levels(factor_vector) <- c("name1", "name2",...)
A good illustration is the raw data that is provided to you by a survey. A common question for every questionnaire is the sex of the respondent. Here, for simplicity, just two categories were recorded, "M" and "F". (You usually need more categories for survey data; either way, you use a factor to store the categorical data.)
survey_vector <- c("M", "F", "F", "M", "M")
Recording the sex with the abbreviations "M" and "F" can be convenient if you are collecting data with pen and paper, but it can introduce confusion when analyzing the data. At that point, you will often want to change the factor levels to "Male" and "Female" instead of "M" and "F" for clarity.
Watch out: the order with which you assign the levels is important. If you type levels(factor_survey_vector), you'll see that it outputs [1] "F" "M". If you don't specify the levels of the factor when creating the vector, R will automatically assign them alphabetically. To correctly map "F" to "Female" and "M" to "Male", the levels should be set to c("Female", "Male"), in this order.
This exercise is part of the course
Introduction to R
Exercise instructions
- Check out the code that builds a factor vector from
survey_vector. You should usefactor_survey_vectorin the next instruction. - Change the factor levels of
factor_survey_vectortoc("Female", "Male"). Mind the order of the vector elements here.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Code to build factor_survey_vector
survey_vector <- c("M", "F", "F", "M", "M")
factor_survey_vector <- factor(survey_vector)
# Specify the levels of factor_survey_vector
levels(factor_survey_vector) <-
factor_survey_vector