'Value' must be a double scalar.

I'm trying to make a function like intersect, union and ismember, but when I let it display the result, I get the error. "'Value' must be a double scalar.".

Here's the code:

function AfiarerezultatButtonPushed(app, event)
app.x = num2str(app.xEditField.Value);
app.y = num2str(app.yEditField.Value);
val = app.AlegereListBox.Value;
switch val
    case 'intersect'
        z = intersect(app.x, app.y);
        app.zEditField.Value = double(z);
        plot(app.UIAxes, z, "bo");
        legend(app.UIAxes, 'x', 'y', 'z');
    case 'union'
        z = union(app.x, app.y);
        app.zEditField.Value = double(z);
    case 'ismember'
        z = ismember(app.y, app.y);
        app.zEditField.Value = double(z);
end

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[DINA]

Error using proiect/AfiarerezultatButtonPushed

'Value' must be a double scalar.

[Benjamin Thompson]

Try setting a breakpoint in your function in MATLAB editor. Find the line causing the error and then fix the code. Looks like something needs to be converted to "double".

Answer 1

[Hassaan]

1. Data Type Conversion: In your code, app.x and app.y are converted to strings with num2str. This is probably not what you want since intersect, union, and ismember functions expect numeric arrays or cell arrays of strings, not string representations of numbers.
2. Plotting Issue: When you're trying to plot z in the intersect case, it might not always be a numeric vector that can be plotted directly, especially if app.x and app.y are strings.
3. Assignment to app.zEditField.Value: You're converting z to a double and then trying to assign it to app.zEditField.Value. This will fail if z is not a single numeric value, but an array or empty.
4. Logic Error in 'ismember': You're using ismember(app.y, app.y) which will always return an array of ones since every element in app.y is a member of app.y. You probably meant ismember(app.x, app.y).

function AfiarerezultatButtonPushed(app, event)
    % Assuming app.xEditField.Value and app.yEditField.Value are numeric
    x = app.xEditField.Value;
    y = app.yEditField.Value;
    val = app.AlegereListBox.Value;
    
    switch val
        case 'intersect'
            z = intersect(x, y);
            updateUIFieldAndPlot(app, z);

        case 'union'
            z = union(x, y);
            updateUIField(app, z);

        case 'ismember'
            z = ismember(x, y);
            updateUIField(app, z);
    end
end

function updateUIField(app, z)
    if length(z) == 1
        app.zEditField.Value = z;
    else
        app.zEditField.Value = num2str(z);
    end
end

function updateUIFieldAndPlot(app, z)
    updateUIField(app, z);
    if isnumeric(z) && ~isempty(z)
        plot(app.UIAxes, z, "bo");
        legend(app.UIAxes, 'x', 'y', 'z');
    end
end

• Proper Data Types: The function now uses the numeric values directly from the EditField components.
• Flexible UI Updates: The updateUIField function sets the zEditField value depending on whether z is a single number or an array.
• Conditional Plotting: The updateUIFieldAndPlot function handles plotting only if z is a numeric and non-empty array.
• Corrected 'ismember' Logic: Now correctly checks if elements of x are in y.

Ensure that your EditField components are indeed providing numeric inputs as expected.

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[DINA]

The error dissapeared but the app don't work. I press on the button and nothing happen.

[DINA]

Error using proiect/updateUIField

'Value' must be a double scalar.

Error in proiect/updateUIFieldAndPlot (line 64)

updateUIField(app, z);

Error in proiect/AfiarerezultatButtonPushed (line 47)

updateUIFieldAndPlot(app, z);