2

I want to get a value from a structure array by code, and I'll have the index stored in a string.

I've tried to run this code:

function M = getdata(matrix,field,varargin)
exp = [];
for i = 1:nargin-3
    exp = [exp num2str(varargin{i}) ','];
end
exp = [exp num2str(varargin{nargin-2})];
M = eval('matrix(exp).(Field)');
end

However, it fails.

For example, suppose I have a structure array with 2 fields, A and B. So, I could write 

MyStruct(1,1).A

A possible use would be: 

M = getdata(MyStruct,A,1,1)

and I want the program to do:

M = MyStruct(1,1).A

How could I do that?

Thanks!

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  • 2
    ...Why not just do M = matrix(varargin{:}).(field)? Commented Nov 14, 2013 at 14:30
  • Because I really want to use getdata with something like: M = getdata(MyStruct,A,1,:) and, if I use the expression you say, I only get one value, not a vector. Commented Nov 14, 2013 at 15:38

2 Answers 2

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2

You can use the getfield function:

M = getfield(MyStruct, {1,1} ,'A');

Or if you wanted, say, MyStruct(1,1).A(3).B:

M = getfield(MyStruct, {1,1}, 'A', {3},'B');
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1 Comment

It fails when one of the indices is :.
0

For the example you give, this will suffice: 

function M = getdata(matrix,field,varargin)
    M = matrix(varargin{:}).(field);

which you call like 

getdata(myStruct, 'A', 1,1)

which makes that function pretty useless.

But, in general, when you have indices given as strings, you can follow roughly the same approach:

%// Your indices
str = {'1', '2'};

%// convert to numbers
str = cellfun(@str2double, str, 'UniformOutput', false);

%// use them as indices into structure
M = myStruct(str{:}).(field)

And if you really insist, your call to eval is just wrong: 

M = eval(['matrix(' exp ').(' field ')']);

And, as a general remark, please refrain from using exp as the name of a variable; it is also the name of a built-in function (the natural exponential function).

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1 Comment

Thank you. Unfortunately, none of the solutions given are useful for me. What I really want to do is using :as index. cellfun is also useless because the conversion from string to cell returns NaN.

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