How to plot a line in Matplotlib with an interval at each data point?

To plot a line in Matplotlib with confidence intervals or error bars at each data point, we can use the fill_between() method to create a shaded region around the main line. This technique is commonly used to show uncertainty or variability in data visualization.

Basic Setup

First, let's understand the key steps involved ?

• Create arrays for means and standard deviations
• Plot the main line using plot() method
• Use fill_between() to create shaded intervals
• Customize appearance with colors and transparency

Example

Here's how to create a line plot with confidence intervals ?

import numpy as np
import matplotlib.pyplot as plt

# Set figure size
plt.rcParams["figure.figsize"] = [7.50, 3.50]
plt.rcParams["figure.autolayout"] = True

# Data points
means = np.array([3, 5, 1, 8, 4, 6])
stds = np.array([1.3, 2.6, 0.78, 3.01, 2.32, 2.9])

# Plot the main line
plt.plot(means, color='red', linewidth=2, label='Mean values')

# Fill the confidence interval
plt.fill_between(range(len(means)), means - stds, means + stds, 
                 alpha=0.3, color='yellow', label='±1 Standard Deviation')

plt.xlabel('Data Points')
plt.ylabel('Values')
plt.title('Line Plot with Confidence Intervals')
plt.legend()
plt.grid(True, alpha=0.3)
plt.show()

Advanced Example with Custom Intervals

You can also create asymmetric intervals or use different confidence levels ?

import numpy as np
import matplotlib.pyplot as plt

# Generate sample data
x = np.linspace(0, 10, 20)
y = np.sin(x) + 0.5 * np.random.randn(20)
error = 0.3 + 0.1 * np.random.randn(20)

plt.figure(figsize=(10, 6))

# Plot main line
plt.plot(x, y, 'o-', color='blue', linewidth=2, markersize=6, label='Data')

# Add confidence intervals
plt.fill_between(x, y - error, y + error, alpha=0.2, color='blue', 
                 label='Confidence Interval')

plt.xlabel('X values')
plt.ylabel('Y values')
plt.title('Line Plot with Variable Confidence Intervals')
plt.legend()
plt.grid(True, alpha=0.3)
plt.show()

Key Parameters

Conclusion

Use fill_between() to create confidence intervals around line plots. Adjust alpha for transparency and choose appropriate colors to make the intervals visually clear without overwhelming the main data line.