# How to highlight outliers in a boxplot in R?

R ProgrammingServer Side ProgrammingProgramming

#### Artificial Intelligence : The Future Of Programming

15 Lectures 54 mins

#### Beyond Basic Programming - Intermediate Python

Most Popular

36 Lectures 3 hours

#### C Programming from scratch- Master C Programming

Best Seller

60 Lectures 8 hours

To highlight outliers in a boxplot, we can create the boxplot with the help of Boxplot function of car package by defining the id.method.

For example, if we have a vector called V then the boxplot of V with highlighted outliers can be created by using the below given command −

Boxplot(~V,id.method="y")

## Example 1

To highlight outliers in a boxplot, use the command given below −

library(car)
x<-c(-10,rnorm(18),10)
Boxplot(~x,id.method="y")
[1] "1" "20"

## Output

If you execute all the above given snippets as a single program, it generates the following output −

## Example 2

To highlight outliers in a boxplot, use the command given below −

grp<-rep(LETTERS[1:4],each=5)
Response<-c(-5,rpois(3,1),10,-8,rpois(3,2),8,-10,rpois(3,2),10,-12,rpois(3,3),12)
Boxplot(Response~grp,id.method="y")
[1] "1" "5" "6" "10" "11" "15" "16" "20"

## Warning message

In Boxplot.default(mf[[response]], x, id = list(method = id.method, −

NAs introduced by coercion

This warning message is displayed because format of the values might not be proper in Response vector but it does not make an impact on the boxplots so we can ignore it.

## Output

If you execute all the above given snippets as a single program, it generates the following output −

Updated on 10-Nov-2021 13:18:52