How to Write a Case Statement in R (With Example)


A case statement is a type of statement that goes through conditions and returns a value when the first condition is met.

The easiest way to implement a case statement in R is by using the case_when() function from the dplyr package:

library(dplyr)

df %>% 
  mutate(new_column = case_when(
    col1 < 9 ~ 'value1',
    col1 < 12 ~ 'value2',
    col1 < 15 ~ 'value3',
    TRUE ~ 'Great'))

This particular function looks at the value in the column called col1 and returns:

  • value1” if the value in col1 is less than 9
  • value2” if the value in col1 is less than 12
  • value3” if the value in col2 is less than 15
  • value4” if none of the previous conditions are true

Note that TRUE is equivalent to an “else” statement.

The following example shows how to use this function in practice.

Example: Case Statement in R

Suppose we have the following data frame in R:

#create data frame
df <- data.frame(player=c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
                 points=c(6, 8, 9, 9, 12, 14, 15, 17, 19, 22))

#view data frame
df

   player points
1       1      6
2       2      8
3       3      9
4       4      9
5       5     12
6       6     14
7       7     15
8       8     17
9       9     19
10     10     22

We can use the following syntax to write a case statement that creates a new column called class whose values are determined by the values in the points column:

library(dplyr) 

#create new column using case statement
df %>% 
  mutate(class = case_when(
    points < 9 ~ 'Bad',
    points < 12 ~ 'OK',
    points < 15 ~ 'Good',
    TRUE ~ 'Great'))

   player points class
1       1      6   Bad
2       2      8   Bad
3       3      9    OK
4       4      9    OK
5       5     12  Good
6       6     14  Good
7       7     15 Great
8       8     17 Great
9       9     19 Great
10     10     22 Great

The case statement looked at the value in the points column and returned:

  • Bad” if the value in the points column was less than 9
  • OK” if the value in the points column was less than 12
  • Good” if the value in the points column was less than 15
  • Great” if none of the previous conditions are true

The new column is called class, since this is the name we specified in the mutate() function.

Additional Resources

The following tutorials explain how to perform other common tasks in R:

How to Use If Statement with Multiple Conditions in R
How to Write a Nested If Else Statement in R
How to Write Your First tryCatch() Function in R

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