Inline Indexing to Dynamic Field Names

Question

Sean 2011-8-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/14863-inline-indexing-to-dynamic-field-names

采纳的回答： Oleg Komarov

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How can I integrate and index function output into dynamic field names?

Example:

Say function y=fun(x) outputs an array of integers.

How can I implement:

Varnames=['var1' 'var2' 'varx' 'vary'];
TestStruct.(Varnames(index(fun(x),3))) = 0;

that is equivalent to: (for instance)

TestStruct.varx = 0;

or better yet, if varx is an array, a way to make it equivalent to:

TestStruct.varx(n) = 0;

Is there a way to tell a function that you are only interested int the nth element?

Thanks in advance,

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Answer 1

Oleg Komarov 2011-9-8

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I felt Walter was a challenge, I shouldn't be suggesting stuff like this...

Varnames = {'var1', 'var2', 'varx', 'vary'};
x = [2 4 1 3];
n = 3;
TestStruct.(Varnames{x*accumarray(n,1,[numel(x),1])}) = 0

or better

s = struct('type','()','subs',{{n}});
TestStruct.(Varnames{subsref(x,s)}) = 0

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Sean 2011-9-28

Thanks Oleg... I had developed my own way of doing this with a custom indexer function, but I much prefer to do it with inbuilt matlab functionality than having extraneous personal functions involved.

The method I used was to add a function equivalent to:

function x=indexer(y,n)

x=y(n);

that I used like:

TestStruct.Varnames{indexer(fun(x),n)} = 0;

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Answer 2

Chaowei Chen 2011-8-31

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/14863-inline-indexing-to-dynamic-field-names#answer_20201

Varnames={'var1', 'var2', 'varx', 'vary'};

%if varx is scalar

TestStruct.(Varnames{1,3}) = 0

%if varx is array

TestStruct=struct(Varnames{1,3},zeros(10,1))

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Jan 2011-9-8

@Sean: You can't. Do not waste time with searching for an inline version. Simply use a FOR loop to access a list of fields.

Walter Roberson 2011-9-8

Well, you can. But it is ugly and obscure and would have even experienced MATLAB programmers trying to figure out what is going on. A simple loop would be shorter, faster, and much much clearer.

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