Bar and histogram plots in MATLAB - Mini Project: Build & Apply

Bar and Histogram Plots

📖 Scenario: You are working as a data analyst and need to visualize sales data and customer age distribution for a small store.

🎯 Goal: Create bar and histogram plots in MATLAB to show sales per product and the age distribution of customers.

📋 What You'll Learn

Create a vector with sales data for 5 products

Create a vector with ages of 20 customers

Plot a bar chart for the sales data

Plot a histogram for the customer ages

💡 Why This Matters

🌍 Real World

Bar charts and histograms are common ways to visualize data in business and research to understand quantities and distributions.

💼 Career

Data analysts and scientists use these plots to communicate insights clearly to teams and decision makers.

1

Create sales data vector

Create a vector called sales with these exact values: [150, 200, 180, 220, 170] representing sales for 5 products.

MATLAB

% Create the sales vector
% Your code here

Hint

Use square brackets to create a vector in MATLAB.

2

Create customer ages vector

Create a vector called ages with these exact values: [22, 25, 30, 22, 28, 35, 40, 22, 30, 27, 25, 29, 31, 33, 28, 26, 24, 30, 29, 27] representing ages of 20 customers.

MATLAB

sales = [150, 200, 180, 220, 170];
% Create the ages vector
% Your code here

Hint

Use square brackets to create the vector with all 20 age values.

3

Plot bar chart for sales

Use the bar function to create a bar chart of the sales vector.

MATLAB

sales = [150, 200, 180, 220, 170];
ages = [22, 25, 30, 22, 28, 35, 40, 22, 30, 27, 25, 29, 31, 33, 28, 26, 24, 30, 29, 27];
% Plot the bar chart for sales
% Your code here

Hint

Use bar(sales) to create the bar chart.

4

Plot histogram for ages

Use the histogram function to create a histogram of the ages vector.

MATLAB

sales = [150, 200, 180, 220, 170];
ages = [22, 25, 30, 22, 28, 35, 40, 22, 30, 27, 25, 29, 31, 33, 28, 26, 24, 30, 29, 27];
bar(sales);
% Plot the histogram for ages
% Your code here

Hint

Use histogram(ages) to create the histogram.

Practice

1. Which of the following best describes the difference between a bar plot and a histogram in MATLAB?

easy

A. Both bar plots and histograms display values for specific categories.

B. Bar plots show data distribution over ranges; histograms display values for specific categories.

C. Both bar plots and histograms show data distribution over ranges.

D. Bar plots display values for specific categories; histograms show data distribution over ranges.

Solution

1. Step 1: Understand bar plot purpose

   Bar plots show values for distinct categories or positions, like sales per month.

2. Step 2: Understand histogram purpose

   Histograms group data into ranges (bins) to show how data spreads, like exam scores distribution.

3. Final Answer:

   Bar plots display values for specific categories; histograms show data distribution over ranges. -> Option D

4. Quick Check:

   Bar = categories, Histogram = ranges [OK]

Hint: Bar = categories, Histogram = data spread [OK]

Common Mistakes:

• Confusing bar plots with histograms
• Thinking both show the same type of data
• Assuming histograms show exact values per category

2. Which MATLAB command correctly creates a bar plot for the vector y = [3, 7, 5]?

easy

A. bar(y)

B. histogram(y)

C. plotbar(y)

D. barplot(y)

Solution

1. Step 1: Identify correct function for bar plot

   The MATLAB function to create a bar plot is bar().

2. Step 2: Check syntax correctness

   Calling bar(y) plots the values in vector y as bars.

3. Final Answer:

   bar(y) -> Option A

4. Quick Check:

   Use bar() for bar plots [OK]

Hint: Use bar() to plot bar charts, histogram() for histograms [OK]

Common Mistakes:

• Using histogram() instead of bar()
• Using non-existent functions like plotbar()
• Incorrect function names or typos

3. What will be the output of the following MATLAB code?

data = [1, 2, 2, 3, 3, 3, 4];
histogram(data, 3)

medium

A. An error because histogram requires vector of edges

B. A histogram with 3 bins showing counts of data in ranges covering 1 to 4

C. A bar plot with bars at positions 1, 2, 3, 4

D. A line plot connecting the data points

Solution

1. Step 1: Understand histogram function with bin count

   Calling histogram(data, 3) creates a histogram with 3 bins dividing the data range.

2. Step 2: Analyze data distribution

   Data ranges from 1 to 4, so bins cover intervals like [1-2), [2-3), [3-4]. Counts show how many values fall in each bin.

3. Final Answer:

   A histogram with 3 bins showing counts of data in ranges covering 1 to 4 -> Option B

4. Quick Check:

   histogram(data, bins) = bins count [OK]

Hint: histogram(data, n) makes n bins for data spread [OK]

Common Mistakes:

• Confusing histogram with bar plot output
• Expecting exact bars at data points
• Thinking histogram needs edges vector always

4. The following MATLAB code is intended to create a bar plot of y = [4, 6, 8], but it produces an error. What is the error?

bar y

medium

A. Incorrect function name; should be histogram

B. Vector y is not defined

C. Missing parentheses around the vector argument

D. bar function cannot plot vectors

Solution

1. Step 1: Check syntax of bar function call

   The correct syntax requires parentheses: bar(y).

2. Step 2: Identify cause of error

   Writing bar y without parentheses causes MATLAB syntax error.

3. Final Answer:

   Missing parentheses around the vector argument -> Option C

4. Quick Check:

   Function calls need parentheses [OK]

Hint: Always use parentheses when calling functions [OK]

Common Mistakes:

• Omitting parentheses in function calls
• Confusing bar with histogram function
• Assuming vector y is undefined without checking

5. You have a dataset of exam scores: scores = [55, 70, 70, 85, 90, 90, 90, 100]. You want to create a histogram with bins of width 10 (like 50-59, 60-69, etc.). Which MATLAB command correctly creates this histogram?

hard

A. histogram(scores, 'BinWidth', 10)

B. bar(scores, 10)

C. histogram(scores, 10)

D. bar(scores, 'BinWidth', 10)

Solution

1. Step 1: Understand how to set bin width in histogram

   Use histogram(data, 'BinWidth', value) to specify bin size.

2. Step 2: Check options for correct syntax

   histogram(scores, 'BinWidth', 10) uses correct syntax to set bin width to 10 for scores.

3. Step 3: Identify incorrect options

   Options B and D use bar function incorrectly; C sets number of bins, not width.

4. Final Answer:

   histogram(scores, 'BinWidth', 10) -> Option A

5. Quick Check:

   Use 'BinWidth' to set histogram bin size [OK]

Hint: Use 'BinWidth' property to set histogram bin size [OK]

Common Mistakes:

• Using bar instead of histogram for bin width
• Passing number instead of 'BinWidth' name-value pair
• Confusing bin count with bin width