How to Drop Levels from a Factor in R - Step by Step Examples

How to Drop Levels from a Factor in R ?

Answer

To drop levels from a factor in R, you can use the droplevels() function, which removes unused levels from a factor. This is useful when you have a factor with levels that are no longer needed or relevant.


✐ Examples

1 Dropping Levels from a Factor Representing Colors

In this example,

  1. We start by creating a character vector named colors which contains the values 'red', 'green', 'blue', 'red', and 'blue'. This vector represents different color categories.
  2. Next, we use the factor() function to convert the colors vector into a factor. We assign the result to a variable named colors_factor. The factor() function automatically identifies the unique levels of the vector, which in this case are 'red', 'green', and 'blue'.
  3. We then subset the colors_factor to include only the first three elements: 'red', 'green', and 'blue'. This removes any occurrence of 'red' and 'blue' in the subset but keeps their levels.
  4. We use the droplevels() function to remove unused levels from the colors_factor. This will drop the levels that are no longer present in the data after subsetting.
  5. We print the modified colors_factor to the console to see the dropped levels. This allows us to verify that the unused levels have been correctly removed from the factor.

R Program

colors <- c('red', 'green', 'blue', 'red', 'blue')
colors_factor <- factor(colors)
colors_factor <- colors_factor[1:3]
colors_factor <- droplevels(colors_factor)
print(colors_factor)

Output

[1] red   green blue 
Levels: green blue

2 Dropping Levels from a Factor Representing Fruits

In this example,

  1. We start by creating a character vector named fruits which contains the values 'apple', 'banana', 'cherry', and 'date'. This vector represents different types of fruits.
  2. Next, we use the factor() function to convert the fruits vector into a factor. We assign the result to a variable named fruits_factor. The factor() function automatically identifies the unique levels of the vector, which in this case are 'apple', 'banana', 'cherry', and 'date'.
  3. We then subset the fruits_factor to include only the first two elements: 'apple' and 'banana'. This removes 'cherry' and 'date' from the subset but keeps their levels.
  4. We use the droplevels() function to remove unused levels from the fruits_factor. This will drop the levels 'cherry' and 'date' that are no longer present in the data after subsetting.
  5. We print the modified fruits_factor to the console to see the dropped levels. This allows us to verify that the unused levels have been correctly removed from the factor.

R Program

fruits <- c('apple', 'banana', 'cherry', 'date')
fruits_factor <- factor(fruits)
fruits_factor <- fruits_factor[1:2]
fruits_factor <- droplevels(fruits_factor)
print(fruits_factor)

Output

[1] apple  banana 
Levels: apple banana

3 Dropping Levels from a Factor Representing Animal Types

In this example,

  1. We start by creating a character vector named animals which contains the values 'dog', 'cat', 'bird', and 'fish'. This vector represents different types of animals.
  2. Next, we use the factor() function to convert the animals vector into a factor. We assign the result to a variable named animals_factor. The factor() function automatically identifies the unique levels of the vector, which in this case are 'dog', 'cat', 'bird', and 'fish'.
  3. We then subset the animals_factor to include only the first three elements: 'dog', 'cat', and 'bird'. This removes 'fish' from the subset but keeps its level.
  4. We use the droplevels() function to remove unused levels from the animals_factor. This will drop the level 'fish' that is no longer present in the data after subsetting.
  5. We print the modified animals_factor to the console to see the dropped levels. This allows us to verify that the unused levels have been correctly removed from the factor.

R Program

animals <- c('dog', 'cat', 'bird', 'fish')
animals_factor <- factor(animals)
animals_factor <- animals_factor[1:3]
animals_factor <- droplevels(animals_factor)
print(animals_factor)

Output

[1] dog  cat  bird 
Levels: dog cat bird

Summary

In this tutorial, we learned How to Drop Levels from a Factor in R language with well detailed examples.


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