Bar and histogram plots in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic difference between a bar plot and a histogram in MATLAB?

A bar plot displays the values of categorical or numerical data as bars with heights representing the values. A histogram shows the distribution of numerical data by grouping data into bins and counting how many values fall into each bin.

beginner

How do you create a simple bar plot for the data vector y = [5, 10, 15] in MATLAB?

Use the command bar(y). This will create vertical bars with heights 5, 10, and 15 respectively.

beginner

Which MATLAB function is used to create a histogram of data?

The function histogram(data) creates a histogram plot showing the distribution of the numerical data.

intermediate

How can you specify the number of bins in a histogram in MATLAB?

You can specify the number of bins by passing a second argument to histogram, for example histogram(data, 10) creates a histogram with 10 bins.

intermediate

What MATLAB command would you use to create a horizontal bar plot?

Use the barh(y) function to create a horizontal bar plot where bars extend horizontally.

Which MATLAB function creates a plot showing the frequency distribution of data?

A plot()

B histogram()

C bar()

D scatter()

The histogram() function groups data into bins and shows frequency distribution.

What does the height of each bar represent in a bar plot?

A The frequency of data points

B The mean of the data

C The value of the data point

D The bin width

In a bar plot, each bar's height corresponds to the actual value of the data point.

How do you change the number of bins in a MATLAB histogram?

A histogram(data, 'NumBins', n)

B bar(data, n)

C histogram(data, n)

D plot(data, n)

You specify the number of bins by passing the 'NumBins' name-value pair argument to histogram.

Which command creates a horizontal bar plot in MATLAB?

A bar(y)

B ploth(y)

C histogram(y)

D barh(y)

barh(y) creates horizontal bars instead of vertical bars.

If you want to visualize categories with their values, which plot is best?

A Bar plot

B Histogram

C Scatter plot

D Pie chart

Bar plots are best for showing values for different categories.

Explain how to create a histogram in MATLAB and how to control the number of bins.

Think about grouping data into ranges and counting how many fall in each.

Describe the difference between a bar plot and a histogram and when to use each.

Consider what each plot tells you about the data.

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