Excel file reading and writing in MATLAB - Step-by-Step Execution

Concept Flow - Excel file reading and writing

Start

↓

Read Excel file

↓

Store data in variable

↓

Process or modify data

↓

Write data back to Excel

↓

End

This flow shows reading data from an Excel file into MATLAB, optionally modifying it, then writing it back to Excel.

Execution Sample

MATLAB

data = readtable('data.xlsx');
data.Var1 = data.Var1 * 2;
writetable(data, 'output.xlsx');

Reads an Excel file into a table, doubles values in column Var1, then writes the table to a new Excel file.

Execution Table

Step	Action	Evaluation	Result
1	Call readtable('data.xlsx')	Reads Excel file	data contains table with Excel data
2	Multiply data.Var1 by 2	Each element in Var1 * 2	data.Var1 updated with doubled values
3	Call writetable(data, 'output.xlsx')	Writes data to Excel	New Excel file 'output.xlsx' created with updated data
4	End	No more commands	Program stops

💡 All steps completed, data read and written successfully

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
data	undefined	Table with original Excel data	Table with Var1 doubled	Table unchanged (written to file)

Key Moments - 3 Insights

Why do we use readtable instead of xlsread?

readtable reads Excel data into a table with column names, making it easier to access and modify data as shown in step 1 of the execution_table.

What happens if the Excel file does not exist when calling readtable?

MATLAB throws an error and stops execution at step 1, so no data is loaded or processed.

Does writetable overwrite the existing Excel file?

Yes, writetable overwrites the file if it exists, as shown in step 3 where 'output.xlsx' is created or replaced.

Visual Quiz - 3 Questions

Look at the execution_table, what does variable 'data' contain after step 1?

A A table with original Excel data

B A doubled numeric array

C An empty variable

D A string with file name

💡 Hint

Check variable_tracker column 'After Step 1' for 'data'

At which step is the Excel file 'output.xlsx' created or overwritten?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

See execution_table row for step 3 describing writetable action

If we skip step 2 (modifying data), what will be the content of 'output.xlsx'?

A Doubled values in Var1

B Empty file

C Original data from 'data.xlsx'

D Error because data is not modified

💡 Hint

Refer to execution_table and variable_tracker to understand data flow

Concept Snapshot

Excel file reading and writing in MATLAB:
- Use readtable('file.xlsx') to read data as a table
- Modify data by accessing table columns (e.g., data.Var1)
- Use writetable(data, 'file.xlsx') to save data back
- writetable overwrites existing files
- Errors occur if input file missing

Full Transcript

This visual execution shows how MATLAB reads data from an Excel file using readtable, stores it in a variable called data, modifies the data by doubling values in one column, and then writes the updated data back to a new Excel file using writetable. The execution table traces each step: reading the file, modifying data, writing the file, and ending. The variable tracker shows how the variable data changes after each step. Key moments clarify common confusions like why readtable is preferred, what happens if the file is missing, and how writetable overwrites files. The quiz tests understanding of variable contents after reading, when the output file is created, and the effect of skipping modification. The snapshot summarizes the main commands and behaviors for Excel file operations in MATLAB.

Practice

1. Which MATLAB function is used to read data from an Excel file into a table?

easy

A. csvread

B. xlswrite

C. readtable

D. load

Solution

1. Step 1: Identify the function for reading Excel files

   MATLAB provides readtable to import Excel data as a table.

2. Step 2: Differentiate from other functions

   xlswrite writes data, csvread reads CSV files, and load loads MAT files.

3. Final Answer:

   readtable -> Option C

4. Quick Check:

   Excel read function = readtable [OK]

Hint: Use readtable to import Excel data as tables quickly [OK]

Common Mistakes:

• Confusing readtable with xlswrite
• Using csvread for Excel files
• Trying to use load for Excel data

2. Which of the following is the correct syntax to write a table T to an Excel file named data.xlsx?

easy

A. readtable('data.xlsx', T)

B. write(T, 'data.xlsx')

C. xlsread('data.xlsx', T)

D. writetable(T, 'data.xlsx')

Solution

1. Step 1: Identify the correct function for writing tables

   The function writetable writes tables to Excel files.

2. Step 2: Check the syntax

   The syntax is writetable(T, 'filename.xlsx'). Other options are either reading functions or incorrect.

3. Final Answer:

   writetable(T, 'data.xlsx') -> Option D

4. Quick Check:

   Write table syntax = writetable(T, filename) [OK]

Hint: Use writetable with table and filename to save Excel files [OK]

Common Mistakes:

• Using write instead of writetable
• Confusing xlsread with writing
• Passing table as second argument to readtable

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

T = readtable('sales.xlsx', 'Sheet', 'Q1', 'Range', 'A1:C5');
disp(height(T));

medium

A. 4

B. 5

C. 3

D. 6

Solution

1. Step 1: Understand the readtable range and header

   The range 'A1:C5' includes 5 rows, but the first row is usually the header.

2. Step 2: Calculate the number of data rows

   Since the first row is header, the data rows are 5 - 1 = 4.

3. Final Answer:

   4 -> Option A

4. Quick Check:

   Rows read minus header = 4 [OK]

Hint: Remember first row is header, so data rows = total rows - 1 [OK]

Common Mistakes:

• Counting header row as data
• Confusing range size with number of rows
• Assuming no header row present

4. Identify the error in this MATLAB code snippet that tries to write a table T to the second sheet of results.xlsx:

writetable(T, 'results.xlsx', 'Sheet', 2, 'Range', 'B2');

medium

A. The 'Sheet' parameter must be a string, not a number

B. The 'Range' parameter cannot be used with writetable

C. The filename must include full path

D. writetable cannot write to Excel files

Solution

1. Step 1: Check the 'Sheet' parameter type

   In writetable, the 'Sheet' argument should be a string with sheet name, not a numeric index.

2. Step 2: Validate other parameters

   'Range' is valid, filename can be relative, and writetable supports Excel files.

3. Final Answer:

   The 'Sheet' parameter must be a string, not a number -> Option A

4. Quick Check:

   Sheet name must be string in writetable [OK]

Hint: Use sheet names as strings, not numbers, in writetable [OK]

Common Mistakes:

• Passing sheet number instead of name
• Thinking Range is invalid for writetable
• Assuming filename needs full path always

5. You want to read only the numeric data from the range B2:D10 in sheet Data of metrics.xlsx into MATLAB as a table. Which code snippet correctly does this and then writes only the first 5 rows back to a new Excel file subset.xlsx?

hard

A. T = readmatrix('metrics.xlsx', 'Sheet', 'Data', 'Range', 'B2:D10');
writetable(T(1:5,:), 'subset.xlsx');

B. T = readtable('metrics.xlsx', 'Sheet', 'Data', 'Range', 'B2:D10');
writetable(T(1:5,:), 'subset.xlsx');

C. T = readtable('metrics.xlsx', 'Sheet', 'Data', 'Range', 'B2:D10');
writetable(T(1:5));

D. T = readmatrix('metrics.xlsx', 'Sheet', 'Data', 'Range', 'B2:D10');
writetable(T, 'subset.xlsx');

Solution

1. Step 1: Read numeric data as a table

   Use readtable with 'Sheet' and 'Range' to get data as a table.

2. Step 2: Write first 5 rows to new Excel file

   Use writetable with T(1:5,:) to write first 5 rows correctly.

3. Final Answer:

   T = readtable('metrics.xlsx', 'Sheet', 'Data', 'Range', 'B2:D10'); writetable(T(1:5,:), 'subset.xlsx'); -> Option B

4. Quick Check:

   readtable + subset rows + writetable = T = readtable('metrics.xlsx', 'Sheet', 'Data', 'Range', 'B2:D10'); writetable(T(1:5,:), 'subset.xlsx'); [OK]

Hint: Use readtable with range, then slice rows before writetable [OK]

Common Mistakes:

• Using readmatrix but then writetable on matrix
• Omitting filename in writetable
• Not slicing rows correctly before writing