Engineering Python · NumPy & pandas Basics
Matplotlib Scatter
In Engineering Python because a two-column table is easier to read as points than as rows — scatter is the first plot after pandas.
A scatter plot places one point per row of two columns. The table below is five (hours, score) pairs — no invented study. `matplotlib.pyplot.scatter` draws those pairs.
- Engineering Python
- Medium level
- 4 concepts
1Two columns become x and y
Each row is one point: the first column is the horizontal value, the second is the vertical value. Both columns must have the same length or the call fails.
The five pairs used here: hours 1,2,3,4,5 with scores 42,55,61,70,78. That is the whole dataset.
No diagram — the idea is carried by the prose, code block or coding lab.
| hours | score |
|---|---|
| 1 | 42 |
| 2 | 55 |
| 3 | 61 |
| 4 | 70 |
| 5 | 78 |
For a scatter of hours vs score, what must be true of the two lists?
- They have the same length — one score per hours value
- They must both be strings
- Score must be longer than hours
Each point needs both coordinates.
2plt.scatter draws the points
`import matplotlib.pyplot as plt` then `plt.scatter(hours, score)` places the points. Label the axes so a reader knows which column is which.
The notebook runtime shows the figure as a cell output. Print the number of points so a stdout check can see the lab ran.
Takeaway
- Idea`import matplotlib.pyplot as plt` then `plt.scatter(hours, score)` places the points. Label the axes so a reader knows which column is which.
Scatter the five pairs
import matplotlib.pyplot as plt
hours = [1, 2, 3, 4, 5]
score = [42, 55, 61, 70, 78]
plt.scatter(hours, score)
plt.xlabel("hours")
plt.ylabel("score")
print(len(hours))Which matplotlib function creates a 2D scatter plot of points (x, y)?
- plt.points(x, y)
- plt.dot_matrix(x, y)
- plt.scatter(x, y)
- plt.grid_plot(x, y)
matplotlib.pyplot.scatter(x, y) renders a scatter plot of markers at coordinates (x, y).
3Each point is one row
The leftmost point is hours=1, score=42. The rightmost is hours=5, score=78. Reading a scatter is reading the table again, with position instead of a grid.
A later ML lab may colour points by a third column. Here there are only two columns — do not invent a third.
Figure. The leftmost pair is hours=1, score=42. The rightmost is hours=5, score=78. Each point is one row of that table, read by position.
Read one point
- Lefthours=1, score=42.
- Righthours=5, score=78.
4Lab: scatter the five pairs
Draw the hours/score scatter and print how many points you plotted.
Figure. Scatter hours [1, 2, 3, 4, 5] against score [42, 55, 61, 70, 78]. That is five points — print len(hours) to show 5.
Takeaway
- IdeaDraw the hours/score scatter and print how many points you plotted.
Coding lab. Five-point scatter runs in the app, with checks on your output.
Notes
- In Engineering Python because a two-column table is easier to read as points than as rows — scatter is the first plot after pandas.
- Each row is one point: the first column is the horizontal value, the second is the vertical value. Both columns must have the same length or the call fails.
- `import matplotlib.pyplot as plt` then `plt.scatter(hours, score)` places the points. Label the axes so a reader knows which column is which.
Exam traps & shortcuts
- Run one cell at a time and read stdout before changing more lines.
- Names are labels for values; rebinding a name does not rewrite old prints.
Recap
Two equal-length columns become points; scatter draws them; each point is a row.
- Two columns become x and y
- Each row is one point: the first column is the horizontal value, the second is the vertical value. Both columns must have the same length or the call fails.
- plt.scatter draws the points
- `import matplotlib.pyplot as plt` then `plt.scatter(hours, score)` places the points. Label the axes so a reader knows which column is which.
- Each point is one row
- The leftmost point is hours=1, score=42. The rightmost is hours=5, score=78. Reading a scatter is reading the table again, with position instead of a grid.
- Lab: scatter the five pairs
- Draw the hours/score scatter and print how many points you plotted.
Practise Matplotlib Scatter
Reading is free and needs no account. Practice, mocks and progress live in the app.
- A 2-question practice set that ends the chapter
- 2 quick checks with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device