Find Structure Field using a string and modify content of data under this field

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Joel Affolter 2019-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/483367-find-structure-field-using-a-string-and-modify-content-of-data-under-this-field

评论： Joel Affolter 2019-10-3

I am currently designing an app, where I want to modify the data of a 1 x 1 structure with 162 fields. The string of the fieldname can be chosen from a dropdown menu and the desired value of said field can be selected via an EditField.

So if, for example I want to change the value of the field "X" to the value "XValue"

app.ValueDropDown.Value = "X"
structure.X = Xvalue

However I want the App to change the value of roughly 50 fields, depending on what the user desires and I currently see no other way than to do that using 50 if functions.

FieldNameVariable = app.ValueDropDown.Value                     %The FieldNameVariable now is of type "Char"
FieldNameVariable = convertCharsToStrings(FieldNameVariable)    %The FieldNameVariable now is of type "String"
if     FieldNameVariable = "X"
    structure.X = XValue
    
else   FileNameVariable  = "X2"
    structure.x2= XValue
    
else   FileNameVariable  = "X3"
    structure.x3= XValue
    
    ...
        
else   FileNameVariable  = "X50"
    structure.x50= XValue
end

Not only is this quite tedious to program, by programming it this way, one does need to change the app code if a new field wants to be made avaible for change.

Does anyone know a way to select and change the values of a certain Field using a string identical to the Field-Name?

Thanks in advance

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Answer 1

Stephen23 2019-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/483367-find-structure-field-using-a-string-and-modify-content-of-data-under-this-field#answer_394585

编辑：Stephen23 2019-10-3

在 MATLAB Online 中打开

You can use dynamic fieldnames:

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

fld = 'X';
S.(fld) = XValue;

ADDENDUM: Given that your example fields are numbered it is quite possible that you would be much better off using a non-scalar structure with indexing:

S(k).Xvalue = XValue;

Using a non-scalar structure with indexing would allow you to set/get the values of multple structure elements at once, and take advantage of other convenient syntaxes:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists