How to Easily Create Heatmaps in Python

heatmap is a type of chart that uses different shades of colors to represent data values.

This tutorial explains how to easily create heatmaps in Python using the seaborn.heatmap function.

Heatmaps in Python

Suppose we have the following dataset in Python that displays the number of sales a certain shop makes during each weekday for five weeks:

import numpy as np
import pandas as pd 
import seaborn as sns

#create a dataset
data = {'day': np.tile(['Mon', 'Tue', 'Wed', 'Thur', 'Fri'], 5),
        'week': np.repeat([1, 2, 3, 4, 5], 5),
        'sales': np.random.randint(0, 50, size=25)

df = pd.DataFrame(data,columns=['day','week','sales'])
df = df.pivot('day', 'week', 'sales')

view first ten rows of dataset

week	 1	 2	 3	 4	 5
Fri	 3	36	12	46	13
Mon	44	39	23	 1	24
Thur	 3	21	24	23	25
Tue	47	 9	 6	38	17
Wed	 0	19	24	39	37

Basic heatmap:

We can create a basic heatmap using the sns.heatmap() function:


Heatmap in Python

The colorbar on the righthand side displays a legend for what values the various colors represent. 

Add lines:

You can add lines between the squares in the heatmap using the linewidths argument:

sns.heatmap(df, linewidths=.5)

Heatmap in seaborn Python

Add annotations:

You can also add annotations to the heatmap using the annot=True argument:

sns.heatmap(df, linewidths=.5, annot=True)

Annotated heatmap in Python

Hide colorbar:

You can also hide the colorbar entirely using the cbar=False option:

sns.heatmap(df, linewidths=.5, annot=True, cbar=False)

Example of a heatmap in Python

Change color theme:

You can also change the color theme using the cmap argument. For example, you could set the colors to range from yellow to green to blue:

sns.heatmap(df, cmap='YlGnBu')

Heatmap python

Or you could have the colors range from red to blue:

sns.heatmap(df, cmap='RdBu')

heatmap with different cmap in Python

For a complete list of colormaps, refer to the matplotlib documentation.

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