Create new fields on structure from char array

Question

Mechrod 2018-3-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/386309-create-new-fields-on-structure-from-char-array

评论： Walter Roberson 2018-3-5

Hi, I have an struct with some char names, and I want each one to became a field in other structure. This is the structure with the names:

This is the structure and the place where I want the names:

I tried several things from Matlab Answers, but nothing works. For example:

arbitrage = struct('Exchanges',list_exchanges);
for ii = 1:15
    newfield = coins(ii).coins;
    arbitrage.(newfield) = 1;
    %arbitrage = setfield(arbitrage,'newfield',[]);
    %[arbitrage(:).newfield] = [];
end

Presents this error:

Scalar structure required for this assignment.

Error in arbitrage_bot_v0_1 (line 21)

arbitrage.(newfield) = 1;

Can someone help me? Thanks.

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Answer 1

Walter Roberson 2018-3-4

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https://ww2.mathworks.cn/matlabcentral/answers/386309-create-new-fields-on-structure-from-char-array#answer_308319

在 MATLAB Online 中打开

[arbitrage.(newfield)] = deal(1);

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Mechrod 2018-3-5

Its incredible how simple details make all the difference. It worked.

Could you quickly explain what was wrong and what your suggestion did? This may help anyone who appears here to check the answer. Thanks!

Walter Roberson 2018-3-5

arbitrage is a nonscalar struct according to the second image header line. arbitrage.(newfield) would undergo expansion as a comma separated list, as that expansion is what is defined for nonscalar struct indexed at a field (or for using {} on a nonscalar cell array with a nonscalar index). To assign to all of the comma expanded fields at the same time you need to list them in [] on the left side of an assignment.

The second half of the trick is using deal() to assign the same value to multiple variables.

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