convert string in app designer to dropbox output

function NoNodesEditFieldValueChanged(app, event)
    app.nN = str2double(app.NoNodesEditField.Value); 
    N_str = num2str((1:app.nN)');
    app.NodeNoDropDown.Items = {(N_str)} ;
    app.NodeNoDropDown_2.Items = num2cell(N_str); 
    app.NodeNoDropDown_3.Items = cellstr(N_str); 
end

The idea is to take a value someone enters (say 7) and create options for the outputs of drop downs that range from 1-7. Currently all methods either end up not working or display NaN

[Geoff Hayes]

Jai - if you put a breakpoint at the line

app.NodeNoDropDown_3.Items = cellstr(N_str)

and then run your code, what is cellstr(N_str)? Is it a cell array of strings?

[Jai Bassi]

When I set the line as a breakpoint, after running the file the drop down becomes the default 'Option 1, Option 2, ...'. . In the debugger it says N_str is a 1 x 3 character of NaN . But if you are asking what I am trying to achieve then yes, I think it needs a cell array of strings as inputs for the drop box? Although I am not 100% certain

Update- I think i ahve it working now thanks. Debugger actually saved me.

New code is :

 function NoNodesEditFieldValueChanged(app, event)
          
            N_str = num2str((1:app.NoNodesEditField.Value)');
            
            app.NodeNoDropDown.Items = cellstr(N_str);
            app.NodeNoDropDown_2.Items = cellstr(N_str); 
            app.NodeNoDropDown_3.Items = cellstr(N_str);
            app.StartNodeDropDown.Items = cellstr(N_str);
            app.EndNodeDropDown.Items = cellstr(N_str);
        end

[Guillaume]

See my comment to Adam's answer for a much better way of generating that list of items (and other recommendations). Do not continue using the code you show which is inefficient.

[Adam Danz]

^^Agreed. Guillaume's compose() suggestion is much more efficient.

I compared the median speeds of 100,000 repetitions of the following lines:

compose('%d', 1:10);
% vs
strsplit(num2str(1:10)); % as suggested in my answer

and compose() was 4x faster (p < 0.0001; wilcoxon signed rank test);

compose('%d', 1:10);
% vs
cellstr(num2str((1:10)')); % as in your code above

and compose() was 5.3x faster (p < 0.0003; wilcoxon signed rank test);

Answer 1

[Adam Danz]

This line is causing the problem

 app.nN = str2double(app.NoNodesEditField.Value); 

because app.NoNodesEditField.Value is already a 'double' and you're treating it as if it were a string which produces a NaN.

This should work:

 function NoNodesEditFieldValueChanged(app, event)
    app.nN = app.NoNodesEditField.Value; 
    app.NodeNoDropDown.Items = strsplit(num2str(1:app.nN))
end

[Guillaume]

app.NoNodesEditField.Value is already a 'double'

It's not been specified if the type of the uieditfield is numeric or text, so Value could be either text or numeric. In this case, it would indeed make sense to use a numeric edit field.

A much better way to generate the Item list would be:

app.NodeNoDropDown.Items = compose('%d', 1:app.nN);  %directly generate the required cell array

I would recommend populating the ItemData property at the same time:

app.NodeNoDropDown.ItemData = 1:app.nN;

This way the Value property returned by the dropdown will be numeric instead of char.

[Adam Danz]

Thanks for the compse() recommendation, that's one I haven't used (yet).

If the uieditfield is numeric and a numeric value is put into str2double(), it would produce a NaN which would propagate through in all of the examples provided by OP. If the uieditfield is text and the string is a number, then the last two options the OP listed should work but the OP says they don't work. That's why I deducted that the uieditfield is numeric (unless it is string and the string is not a number).