Program_11

Author

Asha

Write an R program to generate a basic box plot, enhanced with notches and outliers, and grouped by a categorical variable, using ggplot2.

Step 1: Load required package

We use the ggplot2 package for data visualization.if it’s not already installed, you can install it using:

#install.packages("ggplot2") # Uncomment if needed
library(ggplot2)

Step 2: Use an inbuilt Dataset

We will use the built-in iris dataset.This dataset contains measurements of sepal and petal dimensions for three speciees of iris flowers: - Setosa - Versicolor - Virginica

# Load and preview the dataset
data(iris)
head(iris)

  Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1          5.1         3.5          1.4         0.2  setosa
2          4.9         3.0          1.4         0.2  setosa
3          4.7         3.2          1.3         0.2  setosa
4          4.6         3.1          1.5         0.2  setosa
5          5.0         3.6          1.4         0.2  setosa
6          5.4         3.9          1.7         0.4  setosa

str(iris)

'data.frame':   150 obs. of  5 variables:
 $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
 $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
 $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
 $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
 $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...

The Species column is categorical,making it suitable for grouping, while Sepal.Length is a numerical variable we’ll have to analyze.

Step 3: Create a notched box plot grouped by Species.

We now create a box plot for Sepal.Length,grouped by Species. We’ll enhance the plot using:- Notches to show the confidence interval around the median - Outliers Highlighting using color and shape - Asethetic enhancement like fill color and theme.

ggplot(iris,aes(x=Species,y=Sepal.Length))+
  geom_boxplot(
    notch=TRUE,
    notchwidth=0.6,
    outlier.color = "red",
    outlier.shape = 16,
    fill="skyblue",
    alpha=0.7
  )+
  labs(
    title = "Sepal Length Distribution by Iris Species",
    subtitle = "Box plot with Notches and Outlier Highlighting",
    x="Species",
    y="Sepal Length(cm)"
  )+
  theme_minimal()

Box Plot -Each box summarises the distribution of the Sepal.Lenghtfor a species - showing the interquartile range(IQR) ,median and potential outliers.

Notches -The notches. give a rough 95% confidence interval around the median.If notches of two boxes do not overlap, the medians are significantly different.

Outliers -Points that fall outside 1.5 IQR from the quartiles are considered outliers and shown in red.

Grouping -The plot groups values based on the categorical variable Species , Helping compare between groups.

Aesthetics -theme_minimal()provides a clean background, while colors and transparency make the plot readable.