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How to set colors to a multiple scatter plot in matplotlib?

Onyejiaku Theophilus Chidalu

Overview

The pyplot.scatter() function in matplotlib is used to create a scatter plot. The pyplot module has a function called scatter(), among many other functions, which helps to create or draw scatter plots.

Properties of a scatter plot

  • Uses dots to represent data points but does not join those points with lines.

  • Shows the relationship between two numeric variables. This relation can be used to perform data analysis.

Creating a multiple scatter plot

Before we look at how to set colors to a scatter plot, let’s look at how to create two scatter plots on the same graph.

As mentioned earlier, we use the pyplot.scatter() function in matplotlib, which takes two mandatory arguments:

  • An array of x-coordinates.

  • An array of y-coordinates.

Both of these arrays must be of the same length.

Code

import matplotlib.pyplot as plt
import numpy as np

# x-coordinates for both the scatter plots
x = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

# the first scatter plot
y1 = np.array([10, 50, 30, 40, 50, 25, 70, 15, 90, 65])
plt.scatter(x, y1)

# the second scatter plot
y2 = np.array([5, 35, 40, 45, 80, 20, 95, 55, 70, 10])
plt.scatter(x,y2)

# displaying both plots
plt.show()

Explanation

  • Line 1: In matplotlib, the pyplot module is imported, which will be used to create plots.

  • Line 2: The numpy module is imported, which will be used to create arrays.

  • Line 5: The array x is created, containing the x-coordinates common to both plots.

  • Lines 8 to 9: The array y1 is created, which contains the y-coordinates for the first scatter plot. pyplot.scatter(x,y1) is used to create a scatter plot of x and y1.

  • Lines 12 to 13: The array y2 is created, which contains the y-coordinates for the second scatter plot. pyplot.scatter(x,y2) is used to create a scatter plot of x and y2.

  • Line 16: The pyplot.show() function is used, which tells pyplot to display both the scatter plots.

Note: Notice that the two plots in the figure above gave two different colors. By default, pyplot returned orange and blue.

Setting colors to the multiple scatter plot

To set the colors of a scatter plot, we need to set the argument color or simply c to the pyplot.scatter() function. For example, take a look at the code below:

plt.scatter(x, y, color = 'red')

The above code means that we are setting the color of the scatter plot as red.

Code

import matplotlib.pyplot as plt
import numpy as np

# x-coordinates for both the scatter plots
x = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

# the first scatter plot
y1 = np.array([10, 50, 30, 40, 50, 25, 70, 15, 90, 65])
plt.scatter(x, y1, color = 'red')

# the second scatter plot
y2 = np.array([5, 35, 40, 45, 80, 20, 95, 55, 70, 10])
plt.scatter(x,y2, color = 'green')

# displaying both plots
plt.show()
Output of the code

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Onyejiaku Theophilus Chidalu
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