Program 12

Author

Manoj

Objective

To create a violin plot using ggplot2 in R that displays the distribution of a continuous variable with separate violins for each group using an in-built dataset.

Step 1: Load Required Package

We use the ggplot2 package for plotting. Install it if not already available.

# install.packages("ggplot2") # Uncomment if not installed
library(ggplot2)
Warning: package 'ggplot2' was built under R version 4.1.3

Step 2: Use an Inbuilt Dataset

We’ll use the built-in iris dataset. This dataset includes measurements of sepal and petal lengths/widths for three species of iris flowers.

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 ...

Step 3: Create the Violin Plot

We’ll use geom_violin() from ggplot2, with custom fill and transparency.

ggplot(iris, aes(x = Species, y = Petal.Length, fill = Species)) +
  geom_violin(trim = FALSE, alpha = 0.6, color = "black") +
  labs(
    title = "Distribution of Petal Length by Iris Species",
    x = "Species",
    y = "Petal Length (cm)"
  ) +
  theme_minimal(base_size = 14)

  • Violin Plot: Combines box plot features with a kernel density plot on each side.

  • trim = FALSE: Ensures full density is shown rather than clipped at extreme values.

  • fill = Species: Automatically assigns different fill colors to each group.

  • alpha: Adjusts the transparency.

  • theme_minimal(): Applies a clean layout for the plot.

The violin plot gives a detailed visualization of the distribution and density of the Petal.Length across different Iris species. It’s a powerful alternative to box plots when you want to see the full shape of the distribution.