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Abbreviate acces to struct fields

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Rafael Kübler
Rafael Kübler on 6 Jul 2017
Edited: Jan on 6 Jul 2017
Hello everyone,
i often need to acces a struct field like
sturcture.firstLevel.secondLevel.thirdLevel = 1
Now my question is: Is there a way to abbreviate this long code? Something like defining a pointer.
For example:
sThird = pointer(sturcture.firstLevel.secondLevel.thirdLevel)
Whereas from now I could substitute
sThird
for
sturcture.firstLevel.secondLevel.thirdLevel
Is there a way to do this, so my code is to long?
Thank you for your time reading this.
Rafael

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Accepted Answer

Guillaume
Guillaume on 6 Jul 2017
Edited: Guillaume on 6 Jul 2017
With structures, no it's not possible. Matlab does not support pointers/reference to variables. The workaround is to define a new variable, use that variable to do whatever you wanted to do, and then reassign that variable back to the structure
sThird = structure.firstLevel.secondLevel.thirdLevel;
%do something with sThird
structure.firstLevel.secondLevel.thirdLevel = sThird;
The only other way would be for the content of that thirdLevel field to be a handle class object that wrap whatever it is you store in there. In my opinion, this would be a waste of time just to offer shorter typing in the editor.
edit: forgot another option, which I also don't think is a good idea, use getfield and setfield:
field = {'firstlevel', 'secondlevel', 'thirdLevel'};
value = getfield(structure, field);
setfield(structure, field, someothervalue);

  1 Comment

Jan
Jan on 6 Jul 2017
+1: The first suggestion is perfect. sThird = s.a.b.c creates a shared data copy in Matlab. This means if s.a.b.c is a struct and contains a huge array, the actual data are not duplicated. Therefore this method is fast, even faster than accessing s.a.b.c directly, when it occurres frequently in a loop:
structure.firstLevel.secondLevel.thirdLevel = 17;
tic
for k = 1:1e7
structure.firstLevel.secondLevel.thirdLevel = ...
structure.firstLevel.secondLevel.thirdLevel + m;
end
toc
structure.firstLevel.secondLevel.thirdLevel = 17;
tic
sub2 = structure.firstLevel.secondLevel;
for k = 1:1e7
sub2.thirdLevel = sub2.thirdLevel + m;
end
toc
Elapsed time is 0.053434 seconds.
Elapsed time is 0.036151 seconds.
Well, does not look too impressive for 1e7 iterations.

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