How can I access a field of a struct, if I have a cell-Array containing all the subfields?

I have some problem with a variant control mechanism I need for a simulation.

Suppose I have a struct (named data) that has various fields, possibly containing subfields.

For example: data.car.speed = 10, data.car.color = 'white', data.duration = 1000, data.format = 'A4' etc.

For my variants i have another struct var, that has some of the fields of data that I want to change

For example: var.car.speed = 20, var.duration = 100

In my original simulation I want to have the original data-struct, in my variant1-simulation I want to have a struct of the same composition but with the var-values

For this example: temp_data.car.speed = 20, temp_data.car.color = 'white', temp_data.duration = 100, temp_data.format = 'A4'

It should be noted that I want to use fields and subsequent subfields however I please, so I dont want to be limited by a fixed struct.

I have a working function that utilizes recursion, but it also uses the dreaded eval-function that I like to avoid whenever possible.

function temp_data = include_variants(data, var)
    temp_data = data;
    
    var_toplevel_field = fieldnames(var);
    for i = 1:length(var_toplevel_field)
        if ~isempty(var.(var_toplevel_field{i}))
            temp_data = rekursive_add(temp_data, var, var_toplevel_field(i));
        end
    end
end

function temp_data = rekursive_add(temp_data, var, field_path)
    temp_var = var;
    for i = 1:length(field_path)
        temp_var = temp_var.(field_path{i});
    end
    try 
        next_fields = fieldnames(temp_var);
        for j = 1:length(next_fields)
            temp_data = rekursive_add(temp_data, var, [field_path next_fields{j}]);
        end
    catch
        str = 'temp_data';
        for i = 1:length(field_path)
            str = [str '.' field_path{i}];
        end
        str = [str ' = temp_var;'];
        eval(str)
    end
end

Can anyone think of a way to get this functionality without using eval?

Answer 1

[Steven Lord]

data.car.speed = 10;
data.car.color = 'white';
data.duration = 1000;
data.format = 'A4'

data = struct with fields:
         car: [1×1 struct]
    duration: 1000
      format: 'A4'

pathToField = {'car', 'speed'};
S = getfield(data, pathToField{:})

S = 10

data = setfield(data, pathToField{:}, 42);
disp(data.car)

    speed: 42
    color: 'white'

[Alexander Reich]

Thanks, thats exactly what I was looking for :)