Unrecoginized Fieldname although it should be correctly defined

Hi,

Im trying to create a for loop to shorten my code, but i am running into some issues. My code is as followed:

% Define the joint names

jointNames = {'Knee', 'Ankle', 'Hip', 'Shoulder', 'Elbow'};

% Define the movement directions

directions = {'maxX', 'minX', 'maxY', 'minY', 'maxZ', 'minZ'};

% Initialize a structure to hold the mean angles

meanAngles = struct();

% Loop through each joint and direction

for j = 1:length(jointNames)

jointName = jointNames{j};

for d = 1:length(directions)

direction = directions{d};

% Construct the field name for the data

fieldName = ['RangeAnglesLeft.' direction '.' jointName];

% Calculate the mean angle for each condition (Nwalk and Wwalk)

meanAngleN = mean(cell2mat(Nwalk.(fieldName)));

meanAngleW = mean(cell2mat(Wwalk.(fieldName)));

% Store the mean angles in the structure

fieldMaxName = ['Max' jointName(1:end-1) direction];

fieldMinName = ['Min' jointName(1:end-1) direction];

meanAngles.(fieldMaxName).(['N' fieldMinName]) = meanAngleN;

meanAngles.(fieldMinName).(['W' fieldMaxName]) = meanAngleW;

end

end

Somehow there is an error with the fieldname. The error states: Unrecognized field name "RangeAnglesLeft.maxX.Knee".

Nwalk and Wwalk are a large dataset containing RangeAnglesLeft. This variable is a struct which can retrieve data by being called out as followed: Nwalk.RangeAnglesLeft.maxX.Knee. Somehow in the code above, it tells me that RangeAnglesLeft.maxX.Knee is not recognized. Can anyone help me with this problem?

[Stephen23]

"This variable is a struct which can retrieve data by being called out as followed: Nwalk.RangeAnglesLeft.maxX.Knee"

No, that is exactly the problem: what you have are nested structures, not a structure. Any structure that happens to be stored inside another structure is still its own structure, which requires its own field references.

Once you understand that, then this mistake is easy to avoid.

Answer 1

[Florian Bidaud]

You can't use dots in your fieldname. The dot creates a new field in the structure, but it can't be done directly in the name of the field with a char array or a string.

Instead of

        fieldName = ['RangeAnglesLeft.' direction '.' jointName];
        
        % Calculate the mean angle for each condition (Nwalk and Wwalk)
        meanAngleN = mean(cell2mat(Nwalk.(fieldName)));

You should do something like:

        meanAngleN = mean((Nwalk.RangeAnglesLeft.(direction).(jointName));

Answer 2

[Steven Lord]

As others have said, you cannot index into a multi-level struct array using the .() notation like that. For this you'd probably want to use getfield.

A = struct('x', struct('b', 2, 'c', 3), 'y', 42)

A = struct with fields:
    x: [1×1 struct]
    y: 42

fieldsToRetrieve = {'x', 'c'};
three = getfield(A, fieldsToRetrieve{:}) % Equivalent of A.x.c

three = 3

check = A.x.c

check = 3