Labels, title, and legend in MATLAB - Mini Project: Build & Apply

Labels, title, and legend

📖 Scenario: You are analyzing sales data for two products over a week. You want to create a clear line plot to compare their sales trends.

🎯 Goal: Create a line plot with sales data for two products. Add labels for the x-axis and y-axis, a title for the plot, and a legend to identify each product's line.

📋 What You'll Learn

Create vectors for days and sales data for two products

Add x-axis label as 'Day of Week'

Add y-axis label as 'Sales Units'

Add a title 'Weekly Sales Comparison'

Add a legend with labels 'Product A' and 'Product B'

💡 Why This Matters

🌍 Real World

In business, clear charts help teams understand sales trends quickly and make better decisions.

💼 Career

Data analysts and scientists often create plots with labels, titles, and legends to communicate insights clearly.

1

Create sales data vectors

Create a vector called days with values from 1 to 7 representing days of the week. Create two vectors called salesA and salesB with these exact values: salesA = [50 60 55 70 65 80 75] and salesB = [45 55 60 65 70 75 85].

MATLAB

# Your code here

Hint

Use the colon operator to create days. Assign the exact arrays for salesA and salesB.

2

Plot the sales data

Use the plot function to plot salesA and salesB against days. Use different line styles or colors for each product. Use hold on to plot both lines on the same figure.

MATLAB

days = 1:7;
salesA = [50 60 55 70 65 80 75];
salesB = [45 55 60 65 70 75 85];
% Your code here

Hint

Plot salesA first, then use hold on before plotting salesB.

3

Add labels and title

Add an x-axis label with xlabel('Day of Week'), a y-axis label with ylabel('Sales Units'), and a title with title('Weekly Sales Comparison').

MATLAB

days = 1:7;
salesA = [50 60 55 70 65 80 75];
salesB = [45 55 60 65 70 75 85];
plot(days, salesA, '-o');
hold on;
plot(days, salesB, '-s');
% Your code here

Hint

Use xlabel, ylabel, and title functions with the exact text.

4

Add a legend and display the plot

Add a legend with labels 'Product A' and 'Product B' using the legend function. Then use hold off to finish the plot. Finally, display the plot by running the script.

MATLAB

days = 1:7;
salesA = [50 60 55 70 65 80 75];
salesB = [45 55 60 65 70 75 85];
plot(days, salesA, '-o');
hold on;
plot(days, salesB, '-s');
xlabel('Day of Week');
ylabel('Sales Units');
title('Weekly Sales Comparison');
% Your code here

Hint

Use legend with the exact labels and then hold off to finish.

Practice

1. Which MATLAB function is used to add a label to the x-axis of a plot?

easy

A. xlabel

B. ylabel

C. title

D. legend

Solution

1. Step 1: Understand axis labeling functions

   In MATLAB, xlabel labels the x-axis, ylabel labels the y-axis, title adds a main heading, and legend explains plot lines.

2. Step 2: Identify the function for x-axis label

   The function xlabel is specifically designed to add a label to the x-axis.

3. Final Answer:

   xlabel -> Option A

4. Quick Check:

   Label x-axis = xlabel [OK]

Hint: Use xlabel for x-axis label, ylabel for y-axis [OK]

Common Mistakes:

• Confusing xlabel with ylabel
• Using title instead of axis labels
• Using legend for axis labels

2. Which of the following is the correct syntax to add a legend to a plot with two lines labeled 'Data1' and 'Data2'?

easy

A. legend{'Data1', 'Data2'}

B. legend = ('Data1', 'Data2')

C. legend['Data1', 'Data2']

D. legend('Data1', 'Data2')

Solution

1. Step 1: Recall correct legend syntax

   In MATLAB, the function legend is called with parentheses and string arguments to label plot lines.

2. Step 2: Identify correct syntax

   The correct syntax uses parentheses and comma-separated strings: legend('Data1', 'Data2'). Other options use invalid assignment or brackets.

3. Final Answer:

   legend('Data1', 'Data2') -> Option D

4. Quick Check:

   legend('labels') uses parentheses [OK]

Hint: Use legend('label1', 'label2') with parentheses [OK]

Common Mistakes:

• Using assignment '=' instead of function call
• Using square or curly brackets
• Missing quotes around labels

3. What will be the title of the plot after running this MATLAB code?

plot(1:5, [2 4 6 8 10]);
title('Sales Over Time');

medium

A. plot(1:5, [2 4 6 8 10])

B. Sales Over Time

C. 1:5

D. No title

Solution

1. Step 1: Understand the title function

   The title function sets the main heading of the plot to the given string.

2. Step 2: Check the given code

   The code calls title('Sales Over Time'), so the plot's title will be exactly 'Sales Over Time'.

3. Final Answer:

   Sales Over Time -> Option B

4. Quick Check:

   title('text') sets plot title [OK]

Hint: title('text') sets the plot's main heading [OK]

Common Mistakes:

• Confusing title with axis labels
• Expecting variable values as title
• No title if title function missing

4. Identify the error in this MATLAB code snippet:

plot(x, y);
xlabel = 'Time';
ylabel('Value');
legend('Line1');

medium

A. Using assignment '=' with xlabel instead of function call

B. Missing ylabel function call

C. legend syntax is incorrect

D. plot function is missing arguments

Solution

1. Step 1: Check xlabel usage

   The code uses xlabel = 'Time'; which assigns a string to variable xlabel instead of calling the function xlabel('Time').

2. Step 2: Verify other lines

   ylabel('Value') and legend('Line1') are correctly called as functions. The plot function has arguments x, y assumed defined.

3. Final Answer:

   Using assignment '=' with xlabel instead of function call -> Option A

4. Quick Check:

   Use xlabel('text'), not xlabel = 'text' [OK]

Hint: Call xlabel as function: xlabel('text'), not assignment [OK]

Common Mistakes:

• Assigning xlabel instead of calling function
• Confusing ylabel syntax
• Incorrect legend usage

5. You have plotted two data sets on the same graph using:

plot(x, y1, '-r', x, y2, '-b');

How do you add a title 'Comparison', label the x-axis as 'Time', the y-axis as 'Value', and add a legend with labels 'Data1' and 'Data2'?

hard

A. title = 'Comparison'; xlabel = 'Time'; ylabel = 'Value'; legend = ('Data1', 'Data2');

B. title('Comparison'); xlabel('Time'); ylabel('Value'); legend(['Data1', 'Data2']);

C. title('Comparison'); xlabel('Time'); ylabel('Value'); legend('Data1', 'Data2');

D. title('Comparison'); xlabel('Time'); ylabel('Value'); legend{'Data1', 'Data2'};

Solution

1. Step 1: Use correct function calls for labels and title

   Functions title, xlabel, and ylabel require parentheses with string arguments.

2. Step 2: Use correct legend syntax

   The legend function takes comma-separated strings inside parentheses, not assignment or brackets.

3. Final Answer:

   title('Comparison'); xlabel('Time'); ylabel('Value'); legend('Data1', 'Data2'); -> Option C

4. Quick Check:

   Use function calls with parentheses for labels and legend [OK]

Hint: Use function calls with parentheses for all labels and legend [OK]

Common Mistakes:

• Assigning strings instead of calling functions
• Using brackets or braces for legend
• Missing quotes around labels