How to find values in a nested struct with repeating fieldnames?

I've got a structure, of which I want to extract data. I think a loop in combination with the find function could do the trick, but this seems like an inefficient and error-prone way. Are there any better methods to obtain the same result?

The resulting structure is nested, where the same fieldnames typically repeat on every level. For example:

A = Struct with fields: X, Y, Z

where

Z = Struct with fields: X, Y, Z

My goal is to extract data from fieldname 'Y' when fieldname 'X' returns a specific value. However, this can be on any layer 'Z'. Hence, examples could be:

Solution = A.Z(ii).Y if A.Z(ii).X == searched value

or

Solution = A.Z(ii).Z(jj).Z(kk).Z(ll).Y if A.Z(ii).Z(jj).Z(kk).Z(ll).X == searched value

[Stephen23]

Either loops or recursion, take your pick.

[Oswin Hulsebos]

I was afraid so, thanks!

Answer 1

[Yash]

Hey @Oswin Hulsebos

As @Stephen23 also suggested, recursion would be a good way to do this. Have a look at the example below:

% A is top layer and zVal is under A.Z
zVal = struct('X',2,'Y',4,'Z',struct([]));
A = struct('X',1,'Y',2,'Z',zVal);

% function call
getYIfXisVal(A,2)

ans = 4

% Function for recursion
function yVal = getYIfXisVal(st,val)
    if(st.X==val)
        yVal = st.Y;
    else
        yVal = getYIfXisVal(st.Z,val);
    end
end

I hope this helps!

[Oswin Hulsebos]

This is indeed similar to what I had used so far, and can do the trick, thank you for your help!

Answer 2

[Matt J]

I think a loop in combination with the find function could do the trick, but this seems like an inefficient and error-prone way.

I don't know why you think the find() function would be used here. At most, you would need logical indexing.

As for loops, there is no efficient alternative to looping when dealing with structs and cells. Vectorization is only a thing that applies to numeric arrays,.

[Oswin Hulsebos]

I expected the find to be necessary when the searched value 'X' occurs multiple times, to return the correct indexing in the structure. However, with a recursion this does not seem to be necessary. Thank you for your comment!