Matplotlib is one of the most widely used data visualization libraries in Python. From simple to complex visualizations, it's the go-to library for most.
In this guide, we'll take a look at how to plot a Scatter Plot with Matplotlib.
Scatter Plots explore the relationship between two numerical variables (features) of a dataset.
We'll be using the Ames Housing dataset and visualizing correlations between features from it.
Let's import Pandas and load in the dataset:
import pandas as pd df = pd.read_csv('AmesHousing.csv')
Plot a Scatter Plot in Matplotlib
Now, with the dataset loaded, let's import Matplotlib, decide on the features we want to visualize, and construct a scatter plot:
import matplotlib.pyplot as plt import pandas as pd df = pd.read_csv('AmesHousing.csv') fig, ax = plt.subplots(figsize=(10, 6)) ax.scatter(x = df['Gr Liv Area'], y = df['SalePrice']) plt.xlabel("Living Area Above Ground") plt.ylabel("House Price") plt.show()
Here, we've created a plot, using the PyPlot instance, and set the figure size. Using the returned
Axes object, which is returned from the
subplots() function, we've called the
We need to supply the
y arguments as the features we'd like to use to populate the plot. Running this code results in:
We've also set the x and y labels to indicate what the variables represent. There's a clear positive correlation between these two variables. The more area there is above ground-level, the higher the price of the house was.
There are a few outliers, but the vast majority follows this hypothesis.
Plotting Multiple Scatter Plots in Matplotlib
If you'd like to compare more than one variable against another, such as - check the correlation between the overall quality of the house against the sale price, as well as the area above ground level - there's no need to make a 3D plot for this.
While 2D plots that visualize correlations between more than two variables exist, some of them aren't fully beginner friendly.
An easy way to do this is to plot two plots - in one, we'll plot the area above ground level against the sale price, in the other, we'll plot the overall quality against the sale price.
Let's take a look at how to do that:
import matplotlib.pyplot as plt import pandas as pd df = pd.read_csv('AmesHousing.csv') fig, ax = plt.subplots(2, figsize=(10, 6)) ax.scatter(x = df['Gr Liv Area'], y = df['SalePrice']) ax.set_xlabel("Living Area Above Ground") ax.set_ylabel("House Price") ax.scatter(x = df['Overall Qual'], y = df['SalePrice']) ax.set_xlabel("Overall Quality") ax.set_ylabel("House Price") plt.show()
Here, we've called
2 to indicate that we'd like to instantiate two subplots in the figure.
We can access these via the
Axes instance -
ax refers to the first subplot's axes, while
ax refers to the second subplot's axes.
Here, we've called the
scatter() function on each of them, providing them with labels. Running this code results in:
Plotting a 3D Scatter Plot in Matplotlib
If you don't want to visualize this in two separate subplots, you can plot the correlation between these variables in 3D. Matplotlib has built-in 3D plotting functionality, so doing this is a breeze.
First, we'll need to import the
Axes3D class from
mpl_toolkits.mplot3d. This special type of
Axes is needed for 3D visualizations. With it, we can pass in another argument -
z, which is the third feature we'd like to visualize.
Let's go ahead and import the
Axes3D object and plot a scatter plot against the previous three features:
import matplotlib.pyplot as plt import pandas as pd from mpl_toolkits.mplot3d import Axes3D df = pd.read_csv('AmesHousing.csv') fig = plt.figure() ax = fig.add_subplot(111, projection = '3d') x = df['SalePrice'] y = df['Gr Liv Area'] z = df['Overall Qual'] ax.scatter(x, y, z) ax.set_xlabel("Sale price") ax.set_ylabel("Living area above ground level") ax.set_zlabel("Overall quality") plt.show()
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Running this code results in an interactive 3D visualization that we can pan and inspect in three-dimensional space:
Customizing Scatter Plot in Matplotlib
You can change how the plot looks like by supplying the
scatter() function with additional arguments, such as
ax.scatter(x = df['Gr Liv Area'], y = df['SalePrice'], color = "blue", edgecolors = "white", linewidths = 0.1, alpha = 0.7)
Running this code would result in:
In this tutorial, we've gone over several ways to plot a scatter plot using Matplotlib and Python.
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