Is there a way to extract specific fields from a structure?

Question

TastyPastry 2016-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/291882-is-there-a-way-to-extract-specific-fields-from-a-structure

回答： Itsik Adiv 2018-9-3

I have a 1x1 structure with a large number of fields of which I'd like to extract some subset. I don't want to have to use

[myst.field1 myst.field2 myst.field3]...

Is there a way to shorten the code so I only have to type myst once and just extract the fields necessary? The structure name is nested within another structure so the code can get lengthy.

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Answer 1

Stephen23 2016-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/291882-is-there-a-way-to-extract-specific-fields-from-a-structure#answer_226491

编辑：Stephen23 2016-6-23

在 MATLAB Online 中打开

Solution

>> S.a = 'Hello';
>> S.b = 'World';
>> C = {'a','b'};
>> D = cellfun(@(f)getfield(S,f),C,'UniformOutput',false);
>> horzcat(D{:})
ans = HelloWorld

Take a look at fieldnames.

Improvement

Note that if the fieldnames really are numbered like that then a much better solution would be to consider using a non-scalar array. A non-scalar structure is a much better way to store data, compared to numbered fieldnames. Using a non-scalar structure would avoid having to perform slow and complicated tricks like this, instead you could use the neat and fast methods shown in the link:

>> S(1).f = 'Hello';
>> S(2).f = 'World';
>> [S.f]
ans = HelloWorld

See how choosing the best data storage makes a huge difference to the quality of code!

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TastyPastry 2016-6-23

Oh yeah they're not numbered fieldnames. The issue I'm facing is that the fieldname data is user inputted and comes in random order so I'm trying to avoid indices.

Stephen23 2016-6-23

@TastyPastry: fair enough. Then my solution does exactly what your question asks for: it concatenates the fields together.

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Answer 2

Thorsten 2016-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/291882-is-there-a-way-to-extract-specific-fields-from-a-structure#answer_226485

编辑：Thorsten 2016-6-23

在 MATLAB Online 中打开

help getfield

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TastyPastry 2016-6-23

编辑：TastyPastry 2016-6-23

在 MATLAB Online 中打开

See I did look at getfield(), but it seems like getfield() only works on single fields. I can see that it's able to get the same field for multiple structures in an array and retrieve multiple pieces of data for that field using indexing, but I can't see how it works for multiple fields.

Okay so I tried

getfield(myst,'field1','field2','field3'...);

but that gives me an error Attempt to reference field of non-structure array.

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