CSV file handling in MATLAB

Introduction

CSV files are simple text files that store data in rows and columns. Handling CSV files lets you read data into MATLAB or save your results to share with others.

You want to load data from a spreadsheet into MATLAB for analysis.

You need to save your MATLAB results so others can open them in Excel.

You want to exchange data between MATLAB and other programs easily.

You have data in a text format and want to process it in MATLAB.

You want to create reports or logs in a simple, readable format.

Syntax

MATLAB

data = readmatrix('filename.csv');
writematrix(data, 'filename.csv');

Use readmatrix to read numeric data from a CSV file into a matrix.

Use writematrix to save a matrix or array back to a CSV file.

Examples

Reads numeric data from 'data.csv' into the variable data.

MATLAB

data = readmatrix('data.csv');

Saves the matrix data into a file named 'output.csv'.

MATLAB

writematrix(data, 'output.csv');

Reads data from 'data.csv' into a table, useful for mixed data types.

MATLAB

T = readtable('data.csv');

Writes the table T to a CSV file named 'output.csv'.

MATLAB

writetable(T, 'output.csv');

Sample Program

This program creates a 2x3 matrix, saves it to 'mydata.csv', then reads it back and displays it.

MATLAB

data = [10, 20, 30; 40, 50, 60];
writematrix(data, 'mydata.csv');
readData = readmatrix('mydata.csv');
disp(readData);

Important Notes

If your CSV file contains text or mixed data, use readtable and writetable instead of readmatrix and writematrix.

Make sure the CSV file is in your current folder or provide the full path.

MATLAB automatically handles commas as separators in CSV files.

Summary

Use readmatrix and writematrix for numeric CSV data.

Use readtable and writetable for mixed or text data.

CSV files are easy to share and work with in MATLAB.

Practice

1. Which MATLAB function is best suited to read numeric data from a CSV file into a matrix?

easy

A. csvread

B. readtable

C. readmatrix

D. load

Solution

1. Step 1: Understand the data type

   Numeric data is best handled as a matrix in MATLAB.

2. Step 2: Choose the appropriate function

   readmatrix is designed to read numeric CSV data directly into a matrix.

3. Final Answer:

   readmatrix -> Option C

4. Quick Check:

   Numeric CSV data = readmatrix [OK]

Hint: Use readmatrix for numeric CSV files quickly [OK]

Common Mistakes:

• Using readtable for purely numeric data
• Using load which is for MAT files
• Confusing csvread with readmatrix (csvread is older)

2. Which of the following is the correct syntax to write a matrix A to a CSV file named data.csv in MATLAB?

easy

A. writetable('data.csv', A);

B. writecsv(A, 'data.csv');

C. csvwrite(A, 'data.csv');

D. writematrix(A, 'data.csv');

Solution

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

   writematrix is the modern function to write numeric matrices to CSV files.

2. Step 2: Check syntax correctness

   The syntax writematrix(A, 'data.csv'); correctly specifies the matrix and filename.

3. Final Answer:

   writematrix(A, 'data.csv'); -> Option D

4. Quick Check:

   Write matrix to CSV = writematrix [OK]

Hint: Use writematrix(matrix, filename) to save numeric CSV [OK]

Common Mistakes:

• Using non-existent function writecsv
• Using csvwrite which is outdated
• Using writetable for numeric matrix without conversion

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

A = [1, 2; 3, 4];
writematrix(A, 'test.csv');
B = readmatrix('test.csv');
disp(B);

medium

A. [1 2; 3 4]

B. [1 2 3 4]

C. [1; 2; 3; 4]

D. Error: File not found

Solution

1. Step 1: Write matrix to CSV

   The matrix A is saved as a 2x2 CSV file with rows [1,2] and [3,4].

2. Step 2: Read matrix from CSV

   readmatrix reads the CSV back into the same 2x2 numeric matrix.

3. Final Answer:

   [1 2; 3 4] -> Option A

4. Quick Check:

   Write and read matrix preserves shape [OK]

Hint: writematrix and readmatrix keep matrix shape intact [OK]

Common Mistakes:

• Expecting a single row vector output
• Confusing disp output format with array shape
• Assuming file read error without saving first

4. Consider this MATLAB code snippet:

T = readtable('data.csv');
writetable(T, 'output.csv');

If data.csv contains mixed numeric and text data, what is a common error to watch for?

medium

A. Using csvwrite to write tables causes incorrect output

B. Using writetable on a numeric matrix causes syntax error

C. Forgetting to close the file after reading causes runtime error

D. Using readmatrix instead of readtable causes syntax error

Solution

1. Step 1: Understand data type in CSV

   Mixed numeric and text data require table format to preserve all data correctly.

2. Step 2: Identify correct write function

   csvwrite only supports numeric data and will fail or produce incorrect output for tables.

3. Final Answer:

   Using csvwrite to write tables causes incorrect output -> Option A

4. Quick Check:

   csvwrite not for tables = error [OK]

Hint: Use writetable for mixed data, not csvwrite [OK]

Common Mistakes:

• Using readmatrix for mixed data losing text
• Assuming file must be closed manually in MATLAB
• Using writetable on numeric matrix without conversion

5. You have a CSV file with columns: Name (text), Age (numeric), and Score (numeric). You want to read it, increase all Score values by 10%, and save the updated data back to a CSV file. Which MATLAB code snippet correctly does this?

hard

A. data = csvread('file.csv');
data(:,3) = data(:,3) * 1.1;
csvwrite('file.csv', data);

B. T = readtable('file.csv');
T.Score = T.Score * 1.1;
writetable(T, 'file.csv');

C. T = readtable('file.csv');
T(:,3) = T(:,3) * 1.1;
writetable(T, 'file.csv');

D. A = readmatrix('file.csv');
A(:,3) = A(:,3) * 1.1;
writematrix(A, 'file.csv');

Solution

1. Step 1: Read mixed data correctly

   Use readtable to read CSV with text and numeric columns preserving all data types.

2. Step 2: Update the numeric Score column

   Access the Score column by name and multiply by 1.1 to increase by 10%.

3. Step 3: Save updated table back to CSV

   Use writetable to save the modified table preserving text and numeric data.

4. Final Answer:

   T = readtable('file.csv'); T.Score = T.Score * 1.1; writetable(T, 'file.csv'); -> Option B

5. Quick Check:

   Mixed data update = readtable + modify column + writetable [OK]

Hint: Use readtable and writetable for mixed data updates [OK]

Common Mistakes:

• Using readmatrix loses text column
• Trying to multiply table columns by index incorrectly
• Using csvread/csvwrite which don't support text