Does this variable exist

Hello,

Is it possible to check if a sub variable of a variable existing in the workspace exists?

For exemple 'layers' variables exist in the workspace, how can I put a condition on the existance of layers(k).Weights ?

I know that exist('layers','var') is used to check the existance of variables in workspace.

Thank you! Appreciate any help!

Answer 1

[Stephen23]

For structures:

https://www.mathworks.com/help/matlab/ref/isfield.html

For tables:

https://www.mathworks.com/matlabcentral/answers/132417-equivalent-of-isfield-for-tables

https://www.mathworks.com/matlabcentral/answers/510110-how-to-check-if-a-column-of-a-table-exist

[Steven Lord]

For objects see isprop to determine if the property exists. This is particularly useful for classes with dynamic properties. As an example, define a class:

classdef sometimesX < dynamicprops
    methods
        function obj = addpropX(obj, xval)
            addprop(obj, 'X');
            obj.X = xval;
        end
    end
end

and use that class:

>> y = sometimesX
y = 
  sometimesX with no properties.
  
>> isprop(y, 'X')
ans =
  logical
   0
   
>> y = addpropX(y, 42)
y = 
  sometimesX with properties:

    X: 42

>> isprop(y, 'X')
ans =
  logical
   1

[Andrea Daou]

Thank you for your help! I used isprop and it worked.

Answer 2

[Peter O]

For structures, use isfield()

clear a
a.M = 'hat';
isfield(a,'M') % True
isfield(a,'N') % False

For array size, use length(a) to find the longest dimension of a, or size(a,d) to find the length of the dth dimension (1=row, 2=col, 3=page, 4... etc). To get the total number of elements, use numel(x). Above you are using a struct array. For your use case:

if numel(layers) < k || ~isfield(layers,'Weights')
    % handle undersize struct and/or missing field here
end