MATLAB: Scanning a column in matrix with repeated values

loopsMATLABmatrix

There are four coulmns (Subject, Number, ID, ANS) in a table named 'List'. I initialized a structure with each cell having zero matrices for unique value in subject list based on below code. Once this is done I want to scan the column Subject(which has repeated values) and place the ANS value of each row in the Zero matrix of that subject number at 'IDxNumber' (index). This repeates for every subject value found in the Subject column which is 10 next.
List table
Subject Number ID ANS
9 1 10 -1
9 2 10 1
9 3 10 -1
10 1 5 1
10 2 6 -1
c = 1;
for b = 1:max(List.Subject)
    for a = 1:length(List.Subject)
        if List.Subject(a) == b
            count_id = sum(List.Subject(:) == b);
            Subject_Assist{c} = zeros(101,count_id);
            c = c+1;
        end
   end
end

Best Answer

This code does the initialization. I'm still trying to figure out what you mean about filling it in.
[Edited afterward to fill in.]
% The original data
Subject = [9;9;9;10;10];
Number = [1;2;3;1;2];
ID = [10;10;10;5;6];
ANS = [-1;1;-1;1;-1];
% The original table
List = table(Subject,Number,ID,ANS);
% Find the unique subjects, and their corresponding rows
[uniqueSubject,~,indexFromUniqueBackToAll] = unique(List.Subject);
numberUniqueSubjects = numel(uniqueSubject);
% Create a cell array with one element per subject
output = cell(numberUniqueSubjects,1);
% For each subject ... 
for ns = 1:numberUniqueSubjects
    
    % Index that subject;s rows
    indexThisSubjectsRows = find(indexFromUniqueBackToAll==ns);
    numberRowsThisSubject = numel(indexThisSubjectsRows);
    
    % initialize a matrix of zeros of apprpriate size
    output{ns} = zeros(101,numberRowsThisSubject);
    
    % Fill in ANS at the indicated rows
    for ni = 1:numberRowsThisSubject
        output{ns}(List.ID(indexThisSubjectsRows(ni)),List.Number(indexThisSubjectsRows(ni))) = List.ANS(indexThisSubjectsRows(ni));
    end
    
end
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