How to Manually Add Legends in Matplotlib with Distinct Colors and Labels?

Manually Creating a Legend in Matplotlib

When working with large datasets in matplotlib, manually adding items to the legend with distinct colors and labels can be a useful technique. This prevents duplicates that can arise from automatically including data to the plot.

Original Approach

The original approach attempted to use the following code:

ax2.legend(self.labels, colorList[:len(self.labels)])
plt.legend()

where self.labels is the number of desired legend labels, and colorList is a subset of the colors used in the plot. However, this method yielded no entries in the legend.

Solution

To manually create a legend, the Legend Guide in matplotlib documentation provides a solution. It involves creating a special artist, called a Patch, which can be used as a handle in the legend.

import matplotlib.patches as mpatches
import matplotlib.pyplot as plt

# Create a red patch
red_patch = mpatches.Patch(color='red', label='The red data')

This patch now represents the red data and can be directly added to the legend.

plt.legend(handles=[red_patch])

Adding Multiple Patches

To add multiple colors and labels, the same technique can be applied by creating additional patches.

blue_patch = mpatches.Patch(color='blue', label='The blue data')
plt.legend(handles=[red_patch, blue_patch])

This will result in a legend with two entries, one for each patch.

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