Stop matplotlib repeating labels in legend

Question

Here is a very simplified example:

xvalues = [2,3,4,6]  for x in xvalues:     plt.axvline(x,color='b',label='xvalues')  plt.legend() 

The legend will now show 'xvalues' as a blue line 4 times in the legend. Is there a more elegant way of fixing this than the following?

for i,x in enumerate(xvalues):     if not i:         plt.axvline(x,color='b',label='xvalues')     else:         plt.axvline(x,color='b') 

Answer 1

plt.legend takes as parameters

1. A list of axis handles which are Artist objects
2. A list of labels which are strings

These parameters are both optional defaulting to plt.gca().get_legend_handles_labels(). You can remove duplicate labels by putting them in a dictionary before calling legend. This is because dicts can't have duplicate keys.

For example:

For Python versions < 3.7

from collections import OrderedDict import matplotlib.pyplot as plt  handles, labels = plt.gca().get_legend_handles_labels() by_label = OrderedDict(zip(labels, handles)) plt.legend(by_label.values(), by_label.keys()) 

For Python versions > 3.7

As of Python 3.7, dictionaries retain input order by default. Thus, there is no need for OrderedDict form the collections module.

import matplotlib.pyplot as plt  handles, labels = plt.gca().get_legend_handles_labels() by_label = dict(zip(labels, handles)) plt.legend(by_label.values(), by_label.keys()) 

Docs for plt.legend