JSON to MATLAB Array — Free Online MATLAB Array Converter

What Is MATLAB?

MATLAB (Matrix Laboratory) is a numerical computing environment and programming language developed by MathWorks. It is widely used in engineering, science, finance, and academic research for data analysis, signal processing, control systems, and machine learning.

Key properties:

What Is JSON?

JSON (JavaScript Object Notation) is a lightweight, human-readable text format defined by RFC 8259. It uses key-value pairs and ordered lists to represent structured data.

Why Convert JSON to MATLAB?

MATLAB Data Types for JSON Conversion

MATLAB has three primary data structures for representing JSON data. Choosing the right one depends on your data.

Cell Array

A cell array can hold mixed data types — strings, numbers, booleans, and nested cells. Use this when your JSON contains heterogeneous data.

data = {
   'Alice', 30, true;
   'Bob', 25, false;
   'Charlie', 35, true
};

Numeric Matrix

A numeric matrix (2D array) holds only numbers. Use this when your JSON contains purely numeric data — all strings and booleans are excluded.

data = [
   1, 3.14, 42;
   2, 2.72, 17;
   3, 1.41, 99
];

Struct Array

A struct array uses named fields. Each element is a struct with field names matching the JSON object keys. Use this when you need key-based access.

data(1).name = 'Alice';
data(1).age = 30;
data(2).name = 'Bob';
data(2).age = 25;

JSON-to-MATLAB Type Mapping

Core Features

1. Dual Input Modes

• File Upload: Drag and drop or select a .json file.

• Code Editor: Paste or type raw JSON with syntax highlighting and real-time validation.

2. Variable Name

Set the MATLAB variable name for the output. This becomes the assignment target in the generated code.

% Variable Name = "sensorData"sensorData = {...};

Rules:

• Must start with a letter

• Can contain letters, digits, and underscores

• Case-sensitive

• No spaces or special characters

3. Output Type

Cell Array output:

myData = {
   'Alice', 30, true;
   'Bob', 25, false
};

Numeric Matrix output:

myData = [
   1, 30, 1;
   2, 25, 0
];

Struct Array output:

myData(1).name = 'Alice';
myData(1).age = 30;
myData(1).active = true;
myData(2).name = 'Bob';
myData(2).age = 25;my
Data(2).active = false;

4. String Delimiter

For maximum compatibility, use Single Quote. Use Double Quote if you work with MATLAB's string type (R2017a+).

5. Output Options

Header Comments

Adds comments at the top of the output showing column headers and metadata:

% Generated by A.Tools — JSON To MATLAB Array
% Columns: name, age, active
% Rows: 3
myData = {...};

Transpose

Transposes the output matrix — rows become columns and columns become rows. Useful when:

• You need data organized by column (variable) instead of by row (observation)

• Feeding data into MATLAB functions that expect column vectors

• Matching MATLAB's column-major convention

Without transpose:

data = [
   1, 2, 3;
   4, 5, 6
];
% 2 rows × 3 columns

With transpose:

data = [
   1, 4;
   2, 5;
   3, 6
];
% 3 rows × 2 columns

6. NaN / Missing Value Handling

Controls how JSON null and empty values are represented in MATLAB output:

Example:

% JSON: {"a": 1, "b": null, "c": 3}

% NaN option:
data = [1, NaN, 3];

% '' option (cell array):
data = {1, '', 3};

% [] option:
data = {1, [], 3};

7. Privacy by Design

All processing runs entirely in your browser. No data is uploaded to any server.

How to Use This JSON to MATLAB Array Converter?

Step 1: Provide Your JSON Data

Choose one of two input methods:

• Upload a file: Click "Choose File" and select a .json file, or drag it into the upload area.

• Paste data: Click "Enter Data" to switch to the code editor. Paste your JSON array. A "Valid JSON" badge confirms correct formatting.

Important: The tool expects a JSON array.

Step 2: Configure MATLAB Output

Use the Properties panel on the right:

1. Variable Name: Enter a valid MATLAB variable name (e.g., sensorData, results).

2. Output Type: Select Cell Array (mixed), Numeric Matrix (numbers only), or Struct Array (keyed).

3. String Delimiter: Choose Single Quote (compatible) or Double Quote (R2017a+).

4. Output Options: Check Header Comments and/or Transpose as needed.

5. NaN / Missing: Choose how null/empty values are represented.

Step 3: Convert

Click Convert. The MATLAB code appears in the "Output Data" panel.

Step 4: Copy or Download

• Click Copy to Clipboard to paste into your .m file.

• Premium users can click Download File to save.

Complete Example

Example — Cell Array

Input JSON:

[
   {"name": "Alice", "age": 30, "active": true},
   {"name": "Bob", "age": 25, "active": false},
   {"name": "Charlie", "age": 35, "active": true}
]

Configuration:

• Variable Name: users

• Output Type: Cell Array

• String Delimiter: Single Quote

• Header Comments: On

• Transpose: Off

• NaN / Missing: NaN

Output:

% Generated by A.Tools — JSON To MATLAB Array
% Columns: name, age, active

users = {
   'Alice', 30, true;
   'Bob', 25, false;
   'Charlie', 35, true
};

Example — Numeric Matrix

Input JSON:

[
   {"x": 1.0, "y": 2.5, "z": 0.8},
   {"x": 1.5, "y": 3.0, "z": 1.2},
   {"x": 2.0, "y": 3.5, "z": 0.5},
   {"x": 2.5, "y": 4.0, "z": 1.8}
]

Configuration:

• Variable Name: coords

• Output Type: Numeric Matrix

• Transpose: On

Output:

coords = [
   1.0, 1.5, 2.0, 2.5;
   2.5, 3.0, 3.5, 4.0;
   0.8, 1.2, 0.5, 1.8
];

Example — Struct Array

Input JSON:

[
   {"sensor": "temp_01", "reading": 23.5, "unit": "celsius"},
   {"sensor": "temp_02", "reading": 19.8, "unit": "celsius"},
   {"sensor": "humid_01", "reading": 65.2, "unit": "percent"}
]

Configuration:

• Variable Name: readings

• Output Type: Struct Array

Output:

readings(1).sensor = 'temp_01';
readings(1).reading = 23.5;
readings(1).unit = 'celsius';
readings(2).sensor = 'temp_02';
readings(2).reading = 19.8;
readings(2).unit = 'celsius';
readings(3).sensor = 'humid_01';
readings(3).reading = 65.2;
readings(3).unit = 'percent';

Example — NaN Handling

Input JSON:

[
   {"id": 1, "score": 95, "bonus": 10},
   {"id": 2, "score": null, "bonus": 5},
   {"id": 3, "score": 88, "bonus": null}
]

Configuration:

• Output Type: Numeric Matrix

• NaN / Missing: NaN

Output:

data = [
   1, 95, 10;
   2, NaN, 5;
   3, 88, NaN
];

Filter NaN values in MATLAB:

% Remove rows with any NaN
cleanData = data(~any(isnan(data), 2), :);

jsondecode() vs. This Tool

MATLAB R2016b+ has a built-in jsondecode() function.

Using jsondecode() (Runtime)

jsonStr = fileread('data.json');
data = jsondecode(jsonStr);

Using This Tool (Code Generation)

Real-World Use Cases

Sensor Data Import

% From JSON API response to MATLAB numeric matrix
sensorData = [
   1633036800, 23.5, 45.2, 1013.1;
   1633037100, 23.8, 44.8, 1013.0;
   1633037400, 24.1, 43.5, 1012.8
];

% Plot temperature over time
plot(sensorData(:,1), sensorData(:,2));
xlabel('Timestamp');
ylabel('Temperature (C)');

Experimental Results

results(1).trial = 1;
results(1).accuracy = 0.95;
results(1).loss = 0.12;
results(2).trial = 2;
results(2).accuracy = 0.97;
results(2).loss = 0.08;

Matrix Operations

% Numeric matrix from JSON — ready for linear algebra
A = [
   1, 2, 3;
   4, 5, 6;
   7, 8, 9
];

eigenvalues = eig(A);
rank_A = rank(A);
det_A = det(A);

Frequently Asked Questions (FAQ)

• Does the tool upload my data?

  No. All conversion happens locally in your browser using JavaScript. Your data never leaves your device.

• What is the difference between Cell Array, Numeric Matrix, and Struct Array?

  Cell Array holds mixed types (strings, numbers, booleans) — use for general JSON data. Numeric Matrix holds only numbers — use for pure numeric data. Struct Array uses named fields — use when you need data(1).fieldName access.

• Should I use single or double quotes?

  Use Single Quote ('text') for maximum compatibility with all MATLAB versions. Use Double Quote ("text") only if you need MATLAB's string type (R2017a+).

• What does the Transpose option do?

  It swaps rows and columns. Without transpose, each JSON object becomes a row. With transpose, each JSON field becomes a column vector — matching MATLAB's column-major convention.

• How are null values handled?

  Choose from three options: NaN (numeric not-a-number), '' (empty string), or [] (empty array). NaN is best for numeric matrices; empty string for cell arrays; empty array for general use.

• Can I use this with MATLAB Online?

  Yes. Copy the output and paste it into MATLAB Online or MATLAB desktop.

• What input format is required?

  A JSON array. Arrays of objects produce the best results: [{"key": "value"}, ...]. Arrays of primitives are also supported.

• Is there a file size limit?

  The tool processes data entirely in your browser. Files up to 10 MB typically convert without issues on modern hardware.

• Can I use this on mobile?

  Yes. The tool is responsive and works on smartphones and tablets.