Handling cells which contains structures

Hello community,

I have a question how to nicely handle cells which contain a structure. What I have is a measuerement which is saved as cell. The cell has the following structure: cell.struct.struct.value. To access a specific value I use cell{n, 1}.struct_name.value_name, where n is an index and can go up to 5000. Usually I use this construct to extract the values: cell2mat(cellfun(@(s)s.struct_name.value_name,cell_name,'uni',0)).

In this case this doesn't work since the struct is empty for some indices. Any idea how to solve this without using a for loop?

Thanks Jeremy

[Stephen23]

Often users places structures in cell arrays because they do not realize that structures are arrays too.

You could likely simplify your code:

1. use a structure array (rather than a cell array containing structures)
2. flatten the nested structures as much as possible.

You could then likely use either of these approaches:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

https://www.mathworks.com/help/matlab/ref/getfield.html

Answer 1

[Voss]

% a cell array of structs with some stuff missing:
c = { ...
    struct('field_1',struct('sub_field_1',1)) ...
    struct('field_1',[]) ...
    [] ...
    struct('field_1',struct('sub_field_1',2)) ...
    }

c = 1×4 cell array
    {1×1 struct}    {1×1 struct}    {0×0 double}    {1×1 struct}

% the usual way gives an error in this case:
try
    cell2mat(cellfun(@(s)s.field_1.sub_field_1,c,'uni',0))
catch ME
    disp(ME.message);
end

Dot indexing is not supported for variables of this type.

% use a helper function that checks for the existence of fields:
cell2mat(cellfun(@(s)get_struct_value(s,'field_1','sub_field_1'),c,'uni',0))

ans = 1×2

1 2

% or a different helper function that puts NaNs where struct is empty, etc.:
cell2mat(cellfun(@(s)get_struct_value_with_NaN(s,'field_1','sub_field_1'),c,'uni',0))

ans = 1×4

1 NaN NaN 2

function out = get_struct_value(s,struct_name,value_name)
if isfield(s,struct_name) && isfield(s.(struct_name),value_name)
    out = s.(struct_name).(value_name);
else
    out = []; % any empty struct or struct missing field returns empty array
end
end


function out = get_struct_value_with_NaN(s,struct_name,value_name)
if isfield(s,struct_name) && isfield(s.(struct_name),value_name)
    out = s.(struct_name).(value_name);
else
    out = NaN; % with appropriate place-holder value
end
end

[Jeremy Wayne]

Thanks for the feedback.

Unfortunately it didn't work out for me. So what I just did a loop and replaced all empty structs with a dummy struct.