Summary: Learn how to add legends to plots with secondary axes using the twinx() function in Matplotlib. This guide covers step-by-step instructions and code examples for clear visualization in Python plots.
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Creating clear and informative plots is a fundamental part of data visualization. Matplotlib, a popular plotting library in Python, offers a variety of tools to enhance your plots. One such tool is the twinx() function, which allows you to create a secondary y-axis sharing the same x-axis. However, adding legends to plots with secondary axes can be tricky. This guide will show you how to add legends to such plots effectively.

Understanding twinx()
The twinx() function creates a second y-axis on the right side of the plot, allowing you to plot datasets with different y-ranges on the same x-axis. This is useful for comparing two different datasets that share a common domain but differ in range.

Step-by-Step Guide to Add Legends

Import Libraries
First, ensure you have Matplotlib installed. If not, you can install it using pip install matplotlib.

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Create Sample Data
Let's create some sample data to plot.

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Plot the Data
Create the primary and secondary axes using twinx().

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Combine Legends
To combine legends from both axes, you need to fetch the handles (lines) and labels from both axes and combine them.

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Display the Plot
Finally, show the plot with the combined legend.

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Complete Code Example

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Conclusion
By following these steps, you can create a plot with a secondary y-axis and add a combined legend for both datasets. This method ensures that your plots are clear and informative, enhancing the overall quality of your data visualizations.

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