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How to Create a Single Legend for All Subplots in Matplotlib?
  • Difficulty Level : Medium
  • Last Updated : 23 Dec, 2020

The subplot() function in matplotlib helps to create a grid of subplots within a single figure. In a figure, subplots are created and ordered row-wise from the top left. A legend in the Matplotlib library basically describes the graph elements. The legend() can be customized and adjusted anywhere inside or outside the graph by placing it at various positions. Sometimes it is necessary to create a single legend for all subplots. Below are the examples that show a single legend for all subplots.

Syntax of Subplot():


For example, subplot(2,1,1) is the figure which represents the first subplot with 2 rows and one column, the first subplot lies in the first row.

The subplot(2,1,2) represents the second subplot which lies in the second row in the first column. 

The legend command Syntax:

legend(*args, **kwargs)

If the length of arguments i.e, args is 0 in the legend command then it automatically generates the legend from label properties by calling get_legend_handles_labels() method.

 For example, ax.legend() is equivalent to:

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles, labels)

The get_legend_handles_labels() method returns a tuple of two lists, i.e., list of artists and list of labels. 

Example 1:


# Importing required libraries
import matplotlib.pyplot as plt
import numpy as np
# 2 subplots in 1 row and 2 columns
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(12, 5))
x1 = ['Telugu', 'Hindi', 'English',
      'Maths', 'Science', 'Social']
y1 = [45, 34, 30, 45, 50, 38]
y2 = [36, 28, 30, 45, 38, 48]
# Labels to use in the legend for each line
labels = ["in 2019", "in 2020"]
# Title for subplots
fig.suptitle('Number of Students passed in each subject\
from a class in 2019 & 2020', fontsize=20)
# Creating the sub-plots.
l1 = ax1.plot(x1, y1, color="green")
l2 = ax2.plot(x1, y2, color="blue")
ax1.set_yticks(np.arange(0, 51, 5))
ax2.set_yticks(np.arange(0, 51, 5))
ax1.set_ylabel('Number of students', fontsize=25)
fig.legend([l1, l2], labels=labels,
           loc="upper right")
# Adjusting the sub-plots


Example 2:


# Plotting sub-plots of number of 
# students passed in each subject 
# in academic year 2017-20.
import matplotlib.pyplot as plt
import numpy as np'seaborn'# Plot Styles
fig = plt.figure()
# 4 subplots in 2 rows and 2 columns in a figure
axes = fig.subplots(nrows=2, ncols=2)
axes[0, 0].bar(['Telugu', 'Hindi', 'English'
                'Maths', 'Science', 'Social'],
               [50, 27, 42, 34, 45, 48], 
               color='g', label="Students passed in 2017")
axes[0, 0].set_yticks(np.arange(0, 51, 5))
axes[0, 1].bar(['Telugu', 'Hindi', 'English'
                'Maths', 'Science', 'Social'],
               [50, 27, 42, 34, 45, 48], 
               color='y', label="Students passed in 2018")
axes[0, 1].set_yticks(np.arange(0, 51, 5))
axes[1, 0].bar(['Telugu', 'Hindi', 'English'
                'Maths', 'Science', 'Social'],
               [40, 27, 22, 44, 35, 38],
               color='r', label="Students passed in 2019")
axes[1, 0].set_yticks(np.arange(0, 51, 5))
axes[1, 0].set_xlabel('Subjects', fontsize=25)
# rotating third sub-plot x-axis labels
for tick in axes[1, 0].get_xticklabels():
axes[1, 0].set_ylabel(" Number of Students passed in 2017-2020", fontsize=20)
axes[1, 1].bar(['Telugu', 'Hindi', 'English',
                'Maths', 'Science', 'Social'],
               [40, 27, 32, 44, 45, 48], 
               color='b', label="Students passed in 2020")
axes[1, 1].set_xlabel('Subjects', fontsize=20)
axes[1, 1].set_yticks(np.arange(0, 51, 5))
lines = []
labels = []
for ax in fig.axes:
    Line, Label = ax.get_legend_handles_labels()
    # print(Label)
# rotating x-axis labels of last sub-plot
fig.legend(lines, labels, loc='upper right')

Output :

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