Line colors and width in Matplotlib - Mini Project: Build & Apply

Line colors and width

📖 Scenario: You are working on a simple data visualization project. You want to draw lines on a graph with different colors and thicknesses to make the chart easy to understand.

🎯 Goal: Create a line plot with three lines. Each line should have a specific color and line width as given.

📋 What You'll Learn

Create three lists of y-values for three lines

Create a variable for the x-values

Plot each line with a specific color and line width

Display the plot

💡 Why This Matters

🌍 Real World

Line colors and widths help make charts clearer and easier to read in reports, presentations, and dashboards.

💼 Career

Data scientists and analysts use line styling to highlight important trends and differences in data visualizations.

1

Create data for the lines

Create a list called x with values [1, 2, 3, 4, 5]. Create three lists called y1, y2, and y3 with values [1, 4, 9, 16, 25], [2, 3, 5, 7, 11], and [5, 7, 6, 8, 7] respectively.

Matplotlib

# Create the x values and three y values lists
# Your code here

Hint

Use square brackets to create lists with the exact numbers given.

2

Import matplotlib and set up the plot

Import matplotlib.pyplot as plt. Create a variable called fig, ax by calling plt.subplots().

Matplotlib

x = [1, 2, 3, 4, 5]
y1 = [1, 4, 9, 16, 25]
y2 = [2, 3, 5, 7, 11]
y3 = [5, 7, 6, 8, 7]

# Import matplotlib.pyplot as plt and create fig, ax with plt.subplots()
# Your code here

Hint

Use import matplotlib.pyplot as plt and plt.subplots() to prepare the plot.

3

Plot the lines with colors and widths

Use ax.plot() to plot the three lines with x and y1, y2, y3. Set the line colors to 'red', 'green', and 'blue' respectively. Set the line widths to 2, 4, and 6 respectively.

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y1 = [1, 4, 9, 16, 25]
y2 = [2, 3, 5, 7, 11]
y3 = [5, 7, 6, 8, 7]

fig, ax = plt.subplots()

# Plot y1 with color 'red' and linewidth 2
# Plot y2 with color 'green' and linewidth 4
# Plot y3 with color 'blue' and linewidth 6
# Your code here

Hint

Use color='colorname' and linewidth=number inside ax.plot().

4

Display the plot

Use plt.show() to display the plot with the three colored lines of different widths.

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y1 = [1, 4, 9, 16, 25]
y2 = [2, 3, 5, 7, 11]
y3 = [5, 7, 6, 8, 7]

fig, ax = plt.subplots()

ax.plot(x, y1, color='red', linewidth=2)
ax.plot(x, y2, color='green', linewidth=4)
ax.plot(x, y3, color='blue', linewidth=6)

# Display the plot
# Your code here

Hint

Use plt.show() to open the plot window.

Practice

1. Which parameter in matplotlib.pyplot.plot() changes the color of the line?

easy

A. linestyle

B. color

C. linewidth

D. marker

Solution

1. Step 1: Understand the purpose of parameters in plot()

   The color parameter sets the line color, while linewidth changes thickness.

2. Step 2: Identify the parameter for color

   Among the options, only color directly changes the line color.

3. Final Answer:

   color -> Option B

4. Quick Check:

   Line color = color [OK]

Hint: Remember: color changes color, linewidth changes thickness [OK]

Common Mistakes:

• Confusing linewidth with color
• Using linestyle to change color
• Trying to use marker for color

2. Which of the following is the correct syntax to set a red line with thickness 3 in matplotlib.pyplot.plot()?

easy

A. plt.plot(x, y, color='red', linewidth=3)

B. plt.plot(x, y, linewidth='red', color=3)

C. plt.plot(x, y, color=3, linewidth='red')

D. plt.plot(x, y, width=3, color='red')

Solution

1. Step 1: Check parameter names and values

   The correct parameters are color with a color string and linewidth with a number.

2. Step 2: Validate plt.plot(x, y, color='red', linewidth=3) syntax

   plt.plot(x, y, color='red', linewidth=3) uses color='red' and linewidth=3, which is correct syntax.

3. Final Answer:

   plt.plot(x, y, color='red', linewidth=3) -> Option A

4. Quick Check:

   Correct parameter names and types = plt.plot(x, y, color='red', linewidth=3) [OK]

Hint: Use color='colorname' and linewidth=number [OK]

Common Mistakes:

• Swapping color and linewidth values
• Using wrong parameter names like width
• Passing numbers as color

3. What will be the color and thickness of the line drawn by this code?

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
plt.plot(x, y, color='green', linewidth=5)
plt.show()

medium

A. Blue line with thickness 5

B. Green line with thickness 1

C. Green line with thickness 5

D. Red line with thickness 5

Solution

1. Step 1: Analyze color parameter

   The code sets color='green', so the line color is green.

2. Step 2: Analyze linewidth parameter

   The code sets linewidth=5, so the line thickness is 5 (thicker than default).

3. Final Answer:

   Green line with thickness 5 -> Option C

4. Quick Check:

   color='green' and linewidth=5 = Green line with thickness 5 [OK]

Hint: Check color and linewidth values directly in plot() [OK]

Common Mistakes:

• Ignoring linewidth value
• Assuming default thickness
• Confusing color names

4. Identify the error in this code snippet:

import matplotlib.pyplot as plt
plt.plot([1,2,3], [4,5,6], color=5, linewidth='thick')
plt.show()

medium

A. Missing plt.show() call

B. color should be a number, linewidth should be a string

C. color and linewidth parameters are correct

D. color should be a string, linewidth should be a number

Solution

1. Step 1: Check color parameter type

   color must be a color name string or code, not a number like 5.

2. Step 2: Check linewidth parameter type

   linewidth must be a number (int or float), not a string like 'thick'.

3. Final Answer:

   color should be a string, linewidth should be a number -> Option D

4. Quick Check:

   Parameter types must match expected types [OK]

Hint: color='name', linewidth=number; no numbers for color [OK]

Common Mistakes:

• Passing numbers as color
• Passing strings as linewidth
• Ignoring type errors

5. You want to plot two lines on the same graph: one thick blue line and one thin orange line. Which code correctly does this?

hard

A. plt.plot(x, y1, color='blue', linewidth=6)
plt.plot(x, y2, color='orange', linewidth=1)

B. plt.plot(x, y1, color='orange', linewidth=6)
plt.plot(x, y2, color='blue', linewidth=1)

C. plt.plot(x, y1, linewidth='thick', color='blue')
plt.plot(x, y2, linewidth='thin', color='orange')

D. plt.plot(x, y1, color=6, linewidth='blue')
plt.plot(x, y2, color=1, linewidth='orange')

Solution

1. Step 1: Match colors to lines

   The thick line should be blue, so color='blue' with large linewidth for y1.

2. Step 2: Match thickness and color for second line

   The thin line should be orange, so color='orange' with small linewidth for y2.

3. Step 3: Validate parameter types

   plt.plot(x, y1, color='blue', linewidth=6) plt.plot(x, y2, color='orange', linewidth=1) uses correct parameter names and types for both lines.

4. Final Answer:

   plt.plot(x, y1, color='blue', linewidth=6) plt.plot(x, y2, color='orange', linewidth=1) -> Option A

5. Quick Check:

   Correct colors and linewidths = plt.plot(x, y1, color='blue', linewidth=6) plt.plot(x, y2, color='orange', linewidth=1) [OK]

Hint: Assign color and linewidth clearly for each line [OK]

Common Mistakes:

• Swapping colors and linewidths
• Using strings for linewidth
• Passing numbers as colors