MATLAB: How to extract the field elements of a structure contained in a cell array and store them in a vector

MATLAB

I have a cell array where each cell contains a structure. I want to extract all of the values of a specific structure field and store them in a numeric array. The following is an example of the structure:

myArry{1}.position = 'e';
myArry{1}.color = 'red';
myArry{1}.index = 1;
myArry{2}.position = 'w';
myArry{2}.color = 'orange';
myArry{2}.index = 2;
myArry{3}.position = 'se';
myArry{3}.color = 'blue';
myArry{3}.index = 3;

Best Answer

It is possible to extract and concatenate the field elements of structures contained in a cell array. In order to employ this method without the use of a loop, the structure in each cell must have identical fields.

To extract the “index” field and store it in a vector, use the following syntax:

myStructArry = [myArry{:}];
myIndexArry = [myStructArry.index];

Related Solutions

MATLAB: Matrix storage and extraction inside a cell or a strucutre array.

You can use curly bracket indexing with cell arrays. To extract the content of the second element from cell array 'd', run

b = d{2};

Also, note that you should never create a related variable with different names. So instead of creating a, b, c, and then using for loop to create cell array or struct. It is better to create the cell array to being with. There are ways to create cell array using for-loop using eval(), but it is highly unrecommended in MATLAB. See the reason here: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

MATLAB: Hi, I have set of variables in <1*1 struct> class. Each variables having a data. Is there a way to find out the statistics for each variables which are in struct classes.

Hello Sandeep,

It's not clear what you mean by "statistics", nor what you know about each field of the struct. However, if I were to assume you had something like this:

S = struct('A', rand(3), 'X', rand(4));

so all data in every field in the structure is numeric, and I wanted to compute the size of each matrix, I could do something like:

sizeStruct = struct;
fields = fieldnames(S); % Get all the fields to loop through
for k = 1:numel(fields) % Loop through each field
    f = fields{k};      % Name of the field
    sizeStruct.(f) = size(S.(f));  % Use dynamic field names
end

If you want to avoid a for loop, you can get fancy with cellfun:

S = struct('A', rand(3), 'X', rand(4));
fields = fieldnames(S);
sizeCell = cellfun(@(f) size(S.(f)), fields, 'UniformOutput', false);

Now you have all the data in a cell array, in the same order as the fields cell array. If you want it back into a struct with the same fields as S, you could do the same thing with cellfun, or get fancy with indexing:

C = [fields.' ; sizeCell.'];
sizeStruct = struct(C{:});

Is this the kind of thing you're looking for? If not, what "statistics" do you mean, and what kind of data is contained within the struct?

-Cam

Best Answer

Related Solutions

MATLAB: Matrix storage and extraction inside a cell or a strucutre array.

MATLAB: Hi, I have set of variables in <1*1 struct> class. Each variables having a data. Is there a way to find out the statistics for each variables which are in struct classes.

Related Question