Basic plt.plot usage in Matplotlib - Mini Project: Build & Apply

Basic plt.plot usage

📖 Scenario: You are a data analyst who wants to visualize the sales trend of a small shop over a week. You have the sales numbers for each day and want to create a simple line chart to see how sales changed.

🎯 Goal: Build a simple line plot using matplotlib.pyplot.plot to show sales over days.

📋 What You'll Learn

Create a list called days with values: [1, 2, 3, 4, 5, 6, 7]

Create a list called sales with values: [150, 200, 170, 220, 180, 210, 230]

Use plt.plot(days, sales) to create the line plot

Use plt.show() to display the plot

💡 Why This Matters

🌍 Real World

Line plots are used to visualize trends over time, like sales, temperature, or stock prices.

💼 Career

Data analysts and scientists use matplotlib to create charts that help explain data insights clearly.

1

Create the sales data lists

Create a list called days with values [1, 2, 3, 4, 5, 6, 7] and a list called sales with values [150, 200, 170, 220, 180, 210, 230].

Matplotlib

# Create the days and sales lists
# Your code here

Hint

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

2

Import matplotlib and prepare to plot

Import matplotlib.pyplot as plt to prepare for plotting.

Matplotlib

days = [1, 2, 3, 4, 5, 6, 7]
sales = [150, 200, 170, 220, 180, 210, 230]

# Import matplotlib.pyplot as plt
# Your code here

Hint

Use import matplotlib.pyplot as plt to import the plotting library.

3

Create the line plot

Use plt.plot(days, sales) to create a line plot showing sales over days.

Matplotlib

import matplotlib.pyplot as plt
days = [1, 2, 3, 4, 5, 6, 7]
sales = [150, 200, 170, 220, 180, 210, 230]

# Use plt.plot(days, sales) to create the line plot
# Your code here

Hint

Call plt.plot with days as x-values and sales as y-values.

4

Display the plot

Use plt.show() to display the line plot.

Matplotlib

import matplotlib.pyplot as plt
days = [1, 2, 3, 4, 5, 6, 7]
sales = [150, 200, 170, 220, 180, 210, 230]
plt.plot(days, sales)

# Use plt.show() to display the plot
# Your code here

Hint

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

Practice

1. What does the plt.plot(x, y) function do in matplotlib?

easy

A. It creates a bar chart from x and y data.

B. It clears the current plot.

C. It saves the plot as an image file.

D. It draws a line connecting points defined by x and y data.

Solution

1. Step 1: Understand plt.plot function

   The plt.plot(x, y) function connects points defined by x and y coordinates with lines.

2. Step 2: Differentiate from other functions

   Other options describe different matplotlib functions: bar chart, saving, or clearing plots, which are not done by plt.plot.

3. Final Answer:

   It draws a line connecting points defined by x and y data. -> Option D

4. Quick Check:

   plt.plot connects points with lines [OK]

Hint: Remember: plt.plot connects points with lines [OK]

Common Mistakes:

• Confusing plt.plot with bar chart functions
• Thinking plt.plot saves images
• Assuming plt.plot clears plots

2. Which of the following is the correct syntax to plot y versus x using matplotlib?

easy

A. plt.plot(x = y)

B. plt.plot(y, x)

C. plt.plot(x, y)

D. plt.plot(y)

Solution

1. Step 1: Check the order of parameters in plt.plot

   The first argument is x data, the second is y data, so plt.plot(x, y) is correct.

2. Step 2: Identify incorrect syntax

   Options A uses invalid keyword argument, B reverses x and y, and D misses x data.

3. Final Answer:

   plt.plot(x, y) -> Option C

4. Quick Check:

   Correct order is x then y [OK]

Hint: Plot syntax is plt.plot(x, y) with x first [OK]

Common Mistakes:

• Swapping x and y arguments
• Using invalid keyword arguments
• Providing only one argument without x

3. What will be the output of this code?

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

medium

A. No plot will be shown because plt.show() is missing.

B. A line graph connecting points (1,4), (2,5), and (3,6).

C. A bar chart with bars at x=1,2,3 with heights 4,5,6.

D. A scatter plot of points (1,4), (2,5), and (3,6).

Solution

1. Step 1: Understand plt.plot with x and y lists

   The code plots points (1,4), (2,5), and (3,6) connected by lines.

2. Step 2: Confirm plt.show() displays the plot

   The plt.show() command displays the line graph on screen.

3. Final Answer:

   A line graph connecting points (1,4), (2,5), and (3,6). -> Option B

4. Quick Check:

   plt.plot + plt.show = line graph [OK]

Hint: plt.plot draws lines; plt.show displays them [OK]

Common Mistakes:

• Confusing plt.plot with scatter plot
• Thinking plt.plot creates bar charts
• Forgetting plt.show to display plot

4. Identify the error in this code snippet:

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

medium

A. x and y lists have different lengths causing an error.

B. plt.plot requires only one argument, so two are invalid.

C. plt.show() is missing to display the plot.

D. No error; the plot will display correctly.

Solution

1. Step 1: Check lengths of x and y lists

   x has 3 elements, y has 2 elements; they must be equal length for plt.plot.

2. Step 2: Understand plt.plot requirements

   plt.plot needs x and y lists of same length to pair points; mismatch causes error.

3. Final Answer:

   x and y lists have different lengths causing an error. -> Option A

4. Quick Check:

   Equal length x and y needed [OK]

Hint: x and y must have same length for plt.plot [OK]

Common Mistakes:

• Ignoring length mismatch of x and y
• Thinking plt.plot accepts different length lists
• Assuming plt.show() missing causes error

5. You want to plot two lines on the same graph: y = x and y = x² for x values 0 to 3. Which code correctly does this?

hard

A. plt.plot([0,1,2,3], [0,1,2,3])
plt.plot([0,1,2,3], [0,1,4,9])
plt.show()

B. plt.plot([0,1,2,3], [0,1,4,9])
plt.show()
plt.plot([0,1,2,3], [0,1,2,3])

C. plt.plot([0,1,2,3], [0,1,2,3], [0,1,4,9])
plt.show()

D. plt.plot([0,1,2,3], [0,1,2,3])
plt.show()
plt.plot([0,1,2,3], [0,1,4,9])

Solution

1. Step 1: Plot first line y = x

   Use plt.plot([0,1,2,3], [0,1,2,3]) to plot y = x.

2. Step 2: Plot second line y = x² on same graph

   Use plt.plot([0,1,2,3], [0,1,4,9]) to plot y = x² on same figure before plt.show().

3. Step 3: Call plt.show() once after both plots

   Calling plt.show() displays both lines together.

4. Final Answer:

   plt.plot([0,1,2,3], [0,1,2,3]) plt.plot([0,1,2,3], [0,1,4,9]) plt.show() -> Option A

5. Quick Check:

   Multiple plt.plot calls before plt.show() [OK]

Hint: Call plt.plot twice, then plt.show once [OK]

Common Mistakes:

• Calling plt.show() before all plots
• Trying to plot two lines in one plt.plot call incorrectly
• Plotting lines in wrong order (does not affect but confuses)