Basic Data Visualization

Welcome! In our previous lesson, we focused on data manipulation and transformation using the dplyr library. This allowed us to prepare and refine our datasets. Now, we are moving on to an exciting part of data science: data visualization.

Every data science task involves a data exploration phase, and visualizations are a critical part of this phase. They allow you to visually and more quickly explore the data, detect patterns, and gain insights that might be missed in raw data forms.

In this lesson, you'll learn the foundational concepts of creating visual representations of data in R using the ggplot2 library. Specifically, we'll focus on:

• Scatter Plots: These help you see the relationship between two continuous variables.
• Bar Charts: These are great for comparing categorical data.

ggplot2 is a powerful and widely-used library in R for creating elegant and complex visualizations. It follows the principles of "The Grammar of Graphics", which is a coherent system for describing and building graphs.

To get you started, here's a detailed look at the kind of visualizations you will be creating. We'll be using the famous iris dataset for our examples.

Loading the Data:

First, let's load the iris dataset, which comes pre-loaded in R:

# Load the iris dataset
data(iris)

The iris dataset contains measurements of iris flowers from three different species: setosa, versicolor, and virginica. It includes 150 observations with five variables: Sepal.Length, Sepal.Width, Petal.Length, Petal.Width, and Species.

Creating a Scatter Plot:

Next, we'll create a scatter plot to visualize the relationship between Sepal Length and Sepal Width, colored by species, using ggplot2:

# Scatter Plot
scatter_plot <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width, color = Species)) +
  geom_point() +
  labs(title = "Scatter Plot", x = "Sepal Length", y = "Sepal Width") +
  scale_color_manual(values = c("setosa" = "red", "versicolor" = "green", "virginica" = "blue"))

• ggplot(iris, aes(...)): Initializes the plotting system with the iris dataset and maps Sepal.Length to the x-axis, Sepal.Width to the y-axis, and Species to the color scale.
• geom_point(): Adds points to the plot.
• labs(...): Adds labels for the title, x-axis, and y-axis.
• scale_color_manual: Manually sets colors for species.

Creating a Bar Chart:

Now, let's create a bar chart to visualize the count of each species using ggplot2:

# Bar Chart
bar_chart <- ggplot(iris, aes(x = Species)) +
  geom_bar(fill = "steelblue") +
  labs(title = "Bar Chart of Species", x = "Species", y = "Count")

• ggplot(iris, aes(...)): Initializes the plotting system with the iris dataset and maps Species to the x-axis.
• geom_bar(fill = "steelblue"): Adds bars to the plot with a steel blue fill.
• labs(...): Adds labels for the title, x-axis, and y-axis.

Displaying the Plots:

Finally, you can display the plots using the print function:

# Display plots
print(scatter_plot)
print(bar_chart)

By running the above code, you'll generate a scatter plot showing the relationship between Sepal Length and Sepal Width for different species, and a bar chart showing the count of observations for each species. You should see similar outputs, when running the code: