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

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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.

Accepted Answer

Stephen Cobeldick
Stephen Cobeldick on 23 Jun 2016
Edited: Stephen Cobeldick on 23 Jun 2016
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!
  2 Comments
Stephen Cobeldick
Stephen Cobeldick on 23 Jun 2016
@TastyPastry: fair enough. Then my solution does exactly what your question asks for: it concatenates the fields together.

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More Answers (2)

Thorsten
Thorsten on 23 Jun 2016
Edited: Thorsten on 23 Jun 2016
help getfield
  1 Comment
TastyPastry
TastyPastry on 23 Jun 2016
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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Itsik Adiv
Itsik Adiv on 3 Sep 2018
You can use rmfield instead:
fieldsList = fieldnames(myst); myst = rmfields(myst, fieldnames{4:end});
Of course you can replace indices 4:end with any valid indexing logic you wish

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