How to Plot Multiple Lines in Matplotlib: Simple Guide

To plot multiple lines in matplotlib, call plt.plot() multiple times before plt.show(), or pass multiple sets of x and y data in one plt.plot() call. Each call or data pair creates a new line on the same graph.

Syntax

You can plot multiple lines by calling plt.plot() multiple times or by passing multiple x and y pairs in one call.

• plt.plot(x1, y1): plots the first line
• plt.plot(x2, y2): plots the second line
• plt.show(): displays the graph with all lines

Alternatively:

• plt.plot(x1, y1, x2, y2): plots two lines in one call

python

import matplotlib.pyplot as plt

# Method 1: Multiple plot calls
plt.plot([1, 2, 3], [4, 5, 6])  # First line
plt.plot([1, 2, 3], [6, 5, 4])  # Second line
plt.show()

Example

This example shows how to plot three different lines on the same graph with labels and a legend.

python

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
y1 = [1, 4, 9, 16]
y2 = [2, 3, 5, 7]
y3 = [3, 5, 7, 9]

plt.plot(x, y1, label='Squares')
plt.plot(x, y2, label='Primes')
plt.plot(x, y3, label='Odds')

plt.xlabel('X axis')
plt.ylabel('Y axis')
plt.title('Multiple Lines Example')
plt.legend()
plt.show()

Output

A line graph with three lines labeled Squares, Primes, and Odds, each showing different y-values over x from 1 to 4.

Common Pitfalls

Common mistakes when plotting multiple lines include:

• Not calling plt.show() to display the plot.
• Using mismatched lengths of x and y data arrays, causing errors.
• Overwriting lines by calling plt.plot() without holding the previous plots (usually not an issue in matplotlib).
• Not adding labels or legends, making it hard to distinguish lines.

python

import matplotlib.pyplot as plt

# Wrong: mismatched lengths
# plt.plot([1, 2, 3], [4, 5])  # This will cause an error

# Right: matching lengths
plt.plot([1, 2, 3], [4, 5, 6], label='Line 1')
plt.plot([1, 2, 3], [6, 5, 4], label='Line 2')
plt.legend()
plt.show()

Quick Reference

Tips for plotting multiple lines:

• Use label in plt.plot() to name lines.
• Call plt.legend() to show labels.
• Use different colors or line styles for clarity.
• Always call plt.show() to display the plot.

Key Takeaways

Call plt.plot() multiple times or pass multiple data sets to plot multiple lines.

Always use plt.legend() with labels to identify each line clearly.

Ensure x and y data arrays have the same length to avoid errors.

Call plt.show() once after all lines are plotted to display the graph.

Use different colors or styles to make lines easy to distinguish.