Does this variable exist

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Andrea Daou
Andrea Daou 2020-8-31
评论： Andrea Daou 2020-9-1
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!

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Stephen23
Stephen23 2020-8-31
编辑：Stephen23 2020-8-31
  2 个评论
Steven Lord
Steven Lord 2020-8-31
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
Andrea Daou 2020-9-1
Thank you for your help! I used isprop and it worked.

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更多回答（1 个）

Peter O
Peter O 2020-8-31
编辑：Peter O 2020-8-31
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

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