Bar and histogram plots in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Bar Plot with Custom Colors

What will be the color of the bars in the following MATLAB code?

MATLAB

y = [5 10 15];
bar(y, 'FaceColor', [0 0.5 0]);

A Bars will be red

B Bars will be green with RGB [0 0.5 0]

C Bars will be blue

D Bars will be black

💡 Hint

FaceColor property sets the bar color using RGB values between 0 and 1.

The FaceColor property is set to [0 0.5 0], which means no red, half green, no blue, resulting in a medium green color.

❓ Predict Output

intermediate

Histogram Bin Count Output

What is the output of the following MATLAB code?

MATLAB

data = [1 2 2 3 4 4 4 5];
h = histogram(data, 4);
disp(h.BinCounts);

A [1 2 1 4]

B [1 2 3 2]

C [2 3 2 1]

D [1 3 2 2]

💡 Hint

Bins are automatically spaced to cover the data range with 4 bins.

The data range is from 1 to 5. With 4 bins, the bins cover intervals [1-2), [2-3), [3-4), [4-5]. Counting values in each bin gives [1 2 1 4].

🔧 Debug

advanced

Fix the Error in Bar Plot Code

The following MATLAB code produces an error. Which option fixes it so the bar plot shows correctly?

MATLAB

x = [1 2 3];
y = [4 5];
bar(x, y);

A Change y to have 3 elements: y = [4 5 6];

B Use bar(y) without x: bar(y);

C Change x to have 2 elements: x = [1 2];

D Transpose y: bar(x, y');

💡 Hint

x and y vectors must have the same length for bar(x,y).

The error occurs because x and y have different lengths. Making y length 3 matches x and fixes the error.

📝 Syntax

advanced

Identify Syntax Error in Histogram Code

Which option contains a syntax error in MATLAB histogram plotting?

A histogram(data, 10);

B histogram(data, 'BinWidth', 0.5);

C histogram(data, 'Normalization', 'probability');

D histogram(data, BinWidth=0.5);

💡 Hint

MATLAB uses name-value pairs with quotes, not equal signs.

Option D uses an equal sign (=) which is invalid syntax for name-value pairs in MATLAB. Correct syntax uses comma and quotes.

🚀 Application

expert

Number of Bars in Grouped Bar Plot

Given the following MATLAB code, how many bars will be displayed in the plot?

MATLAB

data = [3 5 2; 4 6 1];
bar(data, 'grouped');

A 2 bars

B 3 bars

C 6 bars

D 9 bars

💡 Hint

Each row is a group, each column is a bar within the group.

The data matrix has 2 rows and 3 columns. Grouped bar plot shows 3 bars per group, 2 groups total, so 6 bars.

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