Matplotlib: how to show legend elements horizontally?

Question

I’d like to set the legend to be displayed horizontally. I do not mean the text of the legend like described in the post Matplotlib legend vertical rotation. My actual case includes an arbitrary number of series specified with a widget. But the following example represents the gist of the challenge:

Snippet:

# Imports
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np

# data
np.random.seed(123)
x = pd.Series(np.random.randn(100),index=pd.date_range('1/1/2000', periods=100)).cumsum()
y = pd.Series(np.random.randn(100),index=pd.date_range('1/1/2000', periods=100)).cumsum()
z = pd.Series(np.random.randn(100),index=pd.date_range('1/1/2000', periods=100)).cumsum()
df = pd.concat([x,y,z], axis = 1)

# plot 
ax = plt.subplot()
for col in (df.columns):
    plt.plot(df[col])
plt.legend(loc="lower left")
plt.xticks(rotation=90)
plt.show()

Plot:

The default layout seems to be vertical.
Looking at the details of help(ax.legend) and the docs , there does not seem to be a straight forward way to change this to horizontal. Or is there?

Edit – Desired Legend: (using MS Paint)

Asked By: vestland

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Source

Answer 1

Specify the ncol parameter in legend. In your case something like:

plt.legend(loc="lower left", ncol=len(df.columns))

This is the only line I changed in your script.

Working full code:

import pandas as pd
import matplotlib.pyplot as plt
import numpy as np

# data
np.random.seed(123)
x = pd.Series(np.random.randn(100),index=pd.date_range('1/1/2000', periods=100)).cumsum()
y = pd.Series(np.random.randn(100),index=pd.date_range('1/1/2000', periods=100)).cumsum()
z = pd.Series(np.random.randn(100),index=pd.date_range('1/1/2000', periods=100)).cumsum()
df = pd.concat([x,y,z], axis = 1)

# plot
ax = plt.subplot()
for col in (df.columns):
    plt.plot(df[col])
plt.legend(loc="lower left", ncol=len(df.columns))
plt.xticks(rotation=90)
plt.show()

Answered By: Francesco Boi

Answer 2

I believe by horizontal, you mean that you want the legend to list the points next to each other instead of vertically.

plt.legend(loc="lower left", mode = "expand", ncol = 3) #expand stretches it along the bottom 
# while ncol specifies the number of columns

https://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.legend

Answered By: mauve

Answer 3

You want to specify the ncol :

plt.legend(loc="lower left", ncol = len(ax.lines) )

Answered By: Ody

Matplotlib: how to show legend elements horizontally?

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