How to Stack a Line Plot on Top of a Bar Plot with Matplotlib

A step-by-step guide on stacking line plots over bar plots in Matplotlib for better data visualization in Python.
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Stack a Line Plot on Top of a Bar Plot with Matplotlib

Visualizing data effectively is critical for drawing insights. One common scenario arises when you want to display two related datasets—like the number of events per year and their percentage representation—on the same graph. In this guide, we will explore how to stack a line plot on top of a bar plot using Matplotlib, a powerful plotting library in Python.

Introduction to the Problem

Imagine you are working on a data analysis project involving geohazards and their occurrences over the years. You have collected data about different types of geohazards and you want to create a visual that not only shows the total number of events each year but also illustrates the percentage of a specific type of geohazard (like droughts) over the same time period.

Understanding the Solution

The solution involves ensuring that both plots are correctly aligned and that their data types are compatible. Below are the steps to successfully stack a line plot on top of a bar plot.

Step 1: Group Your Data

Start by grouping your data to count the number of events by year and hazard type. You can use the Pandas library to achieve this:

[[See Video to Reveal this Text or Code Snippet]]

This organizes your data into a structure suitable for plotting, where each column represents a different hazard type.

Step 2: Calculate Percentages

Next, calculate the percentage of a specific hazard type (drought) per year. Here’s how you can do that:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Create the Bar Plot

Now, create a stacked bar plot using the grouped data. It looks something like this:

[[See Video to Reveal this Text or Code Snippet]]

This code will generate a bar plot displaying the number of events by year, differentiated by hazard type.

Step 4: Create the Line Plot

Here comes the critical part! You need to add a line plot for the percentage of drought events on top of your bar plot. However, before this step, ensure that the indexes of your data are in the correct format. Convert them to strings to avoid mismatches:

[[See Video to Reveal this Text or Code Snippet]]

[[See Video to Reveal this Text or Code Snippet]]

Step 5: Adjust the Layout

Finally, you should adjust the layout to ensure everything fits nicely:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following these steps, you can effectively display a line plot representing percentages on top of a stacked bar plot in Matplotlib. This method not only enhances visual clarity but also makes comparisons between datasets much easier. Remember to always ensure your data is in the correct format and appropriately organized for successful plotting.

Give it a try with your datasets, and you will surely find it helpful for your data visualization needs!