Use Cell Arrays of .NET Data

Cell arrays in MATLAB® are useful for passing object arrays or character arrays to .NET functions as well as for handling jagged array data returned from .NET functions. For more information, see Use MATLAB Arrays with .NET Functions.

Pass Cell Arrays to .NET

When you call a .NET function from MATLAB, you can pass MATLAB cell arrays as arguments.

  • If you pass a cell array of string scalars or character arrays, MATLAB automatically converts the data to a .NET array of strings or objects.

  • If you pass a cell array with elements of other types, MATLAB automatically converts the data to a .NET array of objects.

For more information on the automatic conversion, see Pass MATLAB Cell Arrays to .NET.

However, if you want to pass cell arrays to a .NET function that expects nonrectangular (jagged) arrays, you must explicitly convert the cell arrays to .NET arrays by using the NET.createArray function in MATLAB. For examples, see Pass Jagged Arrays.

Convert Returned .NET Data to MATLAB Cell Arrays

When you call a .NET function from MATLAB, the function can return .NET data that you can convert to a cell array. These examples show how to convert:

  • .NET arrays that contain strings or objects

  • Multidimensional .NET arrays with known data types

  • Nested .NET arrays

Convert System.String[] to Cell Array

To convert .NET System.String and System.Object arrays to MATLAB cell arrays, use the cell function. MATLAB automatically converts the data so that elements of the resulting cell array are of the MATLAB type closest to the .NET type. For data type mapping information, see Handle Data Returned from .NET Objects.

For example, the .NET System.IO.Directory class has a method named GetDirectories that returns a .NET System.String array. Convert the returned .NET array to a cell array of folder names in your C:\ folder.

myList = cell(System.IO.Directory.GetDirectories("C:\"));

Check the data type of converted data.

class(myList)
ans = 
    'cell'

Convert System.Object[,] to Cell Array of Specified Type

If you know the data types of the elements in a System.Object[,] array, you can convert the .NET array to a cell array with elements of a specified data type by using the cell function with the ConvertTypes name-value argument.

A = cell(obj,'ConvertTypes',type)

In that cell function syntax:

  • obj is a .NET System.Object[,] array.

  • type can be one of these values:

    • {'System.DateTime'} — Convert System.DateTime elements to MATLAB datetime elements.

    • {'System.String'} — Convert System.String elements to MATLAB character arrays.

    • {'all'} — Convert all supported .NET types to equivalent MATLAB types.

  • A is a cell array that is the same size as the obj array.

For example, to convert System.DateTime data in a System.Object[,] array named netDates to a cell array of MATLAB datetimes:

mlDates = cell(netDates,'ConvertTypes',{'System.DateTime'})

Convert Nested System.Object[][] Array to Cell Array

MATLAB does not automatically convert a nested System.Object array (that is, a System.Object array contained within another System.Object array). To convert these .NET arrays to cell arrays, call the cell function on each System.Object array.

For example, the sample NetDocCell.cs file defines the MyGraph class and its getNewData method. (To see the C# code in the sample file, see C# NetDocCell.cs File.) The getNewData method returns a System.Object array that contains:

  • A System.String object for the graph label

  • A nested System.Object array that contains:

    • A System.String object for the x-axis label

    • A System.Double array for the y-coordinates

Convert the returned nested array to a cell array that contains all the data:

graph = NetDocCell.MyGraph;
mlData = cell(graph.getNewData)
mlData = 
    [1x1 System.String]    [1x1 System.Object[]]

Then use the cell array to plot the data. To use the data in the cell array, you must convert the individual .NET objects into MATLAB types.

figure(Name=char(mlData{1}))
plot(double(mlData{2}(2)))
xlabel(char(mlData{2}(1)))

Alternatively, you can flatten and organize the nested data by converting each nested .NET array to its own cell array and converting the .NET data to MATLAB variables with MATLAB types. This technique avoids the need to keep track of the different data types and dimensions within one large cell array.

For example, the second element of the mlData cell array is a nested System.Object array. To access the contents of the nested array, create another cell array mlPlotData.

mlPlotData = cell(mlData{2})

mlPlotData = 
    [1x1 System.String]    [1x1 System.Double[]]

Then convert the .NET data into MATLAB types, and store the data as MATLAB variables:

% Convert System.String to char
mytitle = char(mlData{1});
myxlabel = char(mlPlotData{1});
% Convert System.Double to double
y = double(mlPlotData{2});

These additional conversions simplify the code to plot the .NET data:

figure(Name=mytitle)
plot(y)
xlabel(myxlabel)

C# NetDocCell.cs File

The C# example NetDocCell.cs shows how to handle nested System.Object objects. To build and load the NetDocCell assembly, see Build and Load .NET Assembly for MATLAB. The source code is:

using System;
/*
 * C# Assembly used in MATLAB .NET documentation.
 * Method getNewData is used to demonstrate 
 * how MATLAB handles a System.Object 
 * that includes another System.Object.
 */
namespace NetDocCell
{
    public class MyGraph
    {
        public Object[] getNewData()
        /*
         * Create a System.Object array to use in MATLAB examples.
         * Returns containerArr System.Object array containing:
         *  fLabel System.String object
         *  plotData System.Object array containing:
         *      xLabel System.String object
         *      doubleArr System.Double array
        */
        {
            String fLabel = "Figure Showing New Graph Data";
            Double[] doubleArr = { 
								18, 32, 3.133, 44, -9.9, -13, 33.03 };
            String xLabel = "X-Axis Label";
            Object[] plotData = { xLabel, doubleArr };
            Object[] containerArr = { fLabel, plotData };
            return containerArr;
        }
    }
}

See Also

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