MATLAB: Cell contents reference from a non-cell array object ERROR in the following function

Question

function y = edgeindex(edgenum, indexes, id)
length_index = length(indexes);
y = cell(1,edgenum);
    b = 0;
    for i = 1:length_index
        l = indexes(i)
        a = id(1);
        if i == 1
            c = strsplit(char(a),'_');
            b = b+1;
            y{b} = l;
        else
            d = strsplit(char(a),'_');
            if c{3} ~= d{3}
                c = d;
                b=b+1;
                y{b} = l;
            elseif c{3} == d{3}
                y{b} = [y{b}{l}]
              end           
          end
      end

Edgenum – an integer

Indexes – an array of integers

id – is a column vector made of text ex. OUT_218_46_[1][0].

My goal is to be able to create a cell array (y in this case) where each cell includes all of the indexes with the same string between the second and third '_'.

I can't see what is wrong with my code, but I get this error @ y{b} = [y{b} {l}] :

Cell contents reference from a non-cell array object .

Thank you in advance.

Answer 1

= [y{b} (l)] :

The {} are for extracting from a cell and () are for indexing into the elements in the cell since it will not be a cell.