Charts and exploratory analysis

Learning objectives

• Choose a chart that matches a question.
• Label axes and units.
• Identify patterns, gaps, and unusual values.
• Separate observation from explanation.

A first chart

import matplotlib.pyplot as plt

days = ["Mon", "Tue", "Wed", "Thu", "Fri"]
minutes = [20, 35, 25, 40, 30]

plt.bar(days, minutes)
plt.title("Practice time by day")
plt.xlabel("Day")
plt.ylabel("Minutes")
plt.show()

A bar chart compares categories. A line chart is often better for measurements over time, and a histogram shows the shape of a numeric distribution.

Ask before plotting

1. What question is this chart meant to answer?
2. What does each mark represent?
3. Are the axes labeled with units?
4. Is the scale honest and readable?
5. What can we observe, and what would require more evidence?

Practice

Create a line chart for a robot’s distance readings over ten time steps. Add a horizontal line showing the safety threshold. Include a title and a legend.

Checkpoint

Explain why a chart can be technically correct but still misleading. Name one way a truncated axis can change how a difference appears.

See the Matplotlib user guide for chart types and labeling.