Removing empty structure fields Matlab

Question

I'm facing the following problem: I have an array of structures like:

A.B(1,1).x = 'string'
A.B(1,1).y = 12
A.B(1,2).x = []
A.B(1,2).y = []
A.B(1,3).x = 'string2'
A.B(1,3).y = 4

And I would like to remove the empty 2. row from this structure, so that in the end I get fields for (1,1) and (1,3). I was trying to convert to cells, remove and then back to structure, but this way I had to retype names of fields. How is it possible to do it? Can it be done without conversion from structures?

tia!

Answer 1

Use a loop or arrayfun to determine which array elements are empty:

empty_elems = arrayfun(@(s) isempty(s.x) & isempty(s.y),A.B)

returns: [0 1 0]

or

empty_elems = arrayfun(@(s) all(structfun(@isempty,s)), A.B);

which checks if all fields are empty (use any instead of all to check if any element is empty instead of all).

Then remove them using logical indexing:

A.B(empty_elems) = [];

Full solution to your problem in comments:

% find array elements that have all fields empty:
empty_elems = arrayfun(@(s) all(structfun(@isempty,s)), A.B);

% copy non-empty elements to a new array `C`:
C = A.B(~empty_elems);

% find elements of C that have y field >3
gt3_elems = arrayfun(@(s) s.y<3,C);

% delete those form C:
C(gt3_elems) = [];

execute this code step by step and analyze the intermediary variables to understand what's happening. It should be fairly clear.