Bar and histogram plots in MATLAB - Step-by-Step Execution

Concept Flow - Bar and histogram plots

Prepare Data

↓

Choose Plot Type

↓

Bar Plot

↓

Call bar()

↓

Display Plot

↓

Analyze Visual Output

Start with data, pick bar or histogram plot, call the right function, then see the visual output.

Execution Sample

MATLAB

x = [5, 10, 15];
bar(x)

data = randn(1000,1);
histogram(data)

Create a bar plot for fixed values and a histogram for random data distribution.

Execution Table

Step	Action	Input Data	Function Called	Plot Type	Output Description
1	Prepare data for bar plot	[5, 10, 15]	None	None	Data array ready
2	Call bar()	[5, 10, 15]	bar(x)	Bar plot	Bars at heights 5, 10, 15 displayed
3	Prepare data for histogram	1000 random normal values	None	None	Random data generated
4	Call histogram()	random data	histogram(data)	Histogram plot	Histogram showing data distribution displayed
5	End of plotting	N/A	N/A	N/A	Plots shown on figure window

💡 All plotting commands executed, figures displayed.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
x	undefined	[5, 10, 15]	[5, 10, 15]	[5, 10, 15]
data	undefined	undefined	1000 random values	1000 random values

Key Moments - 2 Insights

Why does bar(x) show bars at specific heights instead of a distribution?

Because bar() treats the input as heights of bars at positions 1, 2, 3, not as data to bin like histogram(). See execution_table step 2.

How does histogram(data) decide the number of bins?

Histogram uses default binning rules to group data into ranges. This is automatic unless specified. See execution_table step 4 where histogram() is called.

Visual Quiz - 3 Questions

Look at the execution table, what is the input data when bar() is called?

A [5, 10, 15]

B 1000 random values

C Empty array

D Single number 5

💡 Hint

Check execution_table row 2 under 'Input Data'

At which step does the histogram plot get displayed?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at execution_table row 4 under 'Plot Type'

If you change x to [1,2,3,4], how does the bar plot output change?

A Bars at heights 1,2,3,4 displayed

B Histogram with 4 bins displayed

C No plot displayed

D Bars at heights 5,10,15 displayed

💡 Hint

Refer to variable_tracker for x values and execution_table step 2

Concept Snapshot

Bar and histogram plots in MATLAB:
- Use bar(x) to plot bars with heights from vector x.
- Use histogram(data) to plot data distribution.
- Bar plots show exact values; histograms group data into bins.
- Both display in figure windows automatically.
- Customize bins in histogram() if needed.

Full Transcript

This visual execution shows how to create bar and histogram plots in MATLAB. First, data is prepared: a vector x for bar plot and random data for histogram. Then bar(x) is called to display bars at heights 5, 10, and 15. Next, histogram(data) is called to show the distribution of 1000 random values. Variables x and data change as shown in the tracker. Key points include understanding bar plots show exact values as bars, while histograms group data into bins automatically. The quiz checks understanding of inputs and outputs at each step.

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