MATLAB: Using structfun with nested structures

non-scalarstructfun

Hi everyone,

I have an overarching structure, with nested substructure, in the following format:

overarching(k).nested

with k=1:8. These nested structures have different sizes, and I was trying to compute the size of each nested structure using structfun as follows:

nested_size=structfun(@size,overarching,'UniformOutput',0)

However, the input structure is non-scalar, and it does not work. I can get the size of each nested structure using a loop to iterate on the nested structures, but I would like to avoid loops if possible. Is there a way of doing this using structfun, that I am not aware of?

Thank you in advance for your help!

Best Answer

The structfun function only works on scalar struct arrays, iterating over the fields of that scalar struct. While you could use arrayfun, it may be easier to understand (and perform just as well) if you use a for loop. I know people have said "Don't use for loops in MATLAB, they're slow." While that may have been true in the past (and you can still write a for loop so it is slow in current MATLAB) the performance of for loops have increased significantly with the improvements we have made to MATLAB over the years.

Besides a for loop over 8 elements of a struct array calling size is highly unlikely, in my experience, to be the bottleneck in your code.

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MATLAB: How to repeat rows in fields of structure

Note that practically, there is no difference between arrayfun, structfun, etc. and a loop. If anything, arrayfun can be slower than a loop.

I suspect that what you want is structfun which applies the same function to each field of the structure:

news = structfun(@(fld) repmat(fld, 53, 1), s, 'UniformOutput', false)

MATLAB: Assign value to field of nested structure in a structure array

That's one of the downside of multilevel structures. As Jan says, it's not possible to assign at once to fields of a substructure.

More importantly, note that when you grow the root source structure (by adding the first names of the 4 persons, only the 1st element of the structure array is a FamilyInfo substructure. The other 3 are initialised empty, because matlab does not copy the type of fields when it grows structure arrays. So if you actually want to have the correct FamilyInfo substructure after growing, you actually need to deal a FamilyInfo field to each element. You may as well set the value of NumberOfSiblings to the correct one:

[person.FamilyInfo] = deal(struct('FatherName',[],'MotherName',[],'NumberOfsiblings',3);

Note that if you want to avoid losing the FamilyInfo struct, don't grow the array but initialise it at the correct size to start with:

numpersons = 4;
person = struct('First_Name',[],'Last_Name',[],...
'FamilyInfo',repmat({struct('FatherName',[],'MotherName',[],'NumberOfsiblings',[])}, 1, numpersons));

Best Answer

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