Create dynamic array by comparing the new incoming variable value

I am creating a dynamically allocated 2D array in which 1st column is the header column indicating the Step Number(a variable). I have to compare the incoming new value with all the Step Numbers i.e. 1st column and if I get a match assign that value to that column. If no matching column value is found, a new column with that value is created. Can anyone help me with this.?

Answer 1

[Jan]

Letting an array grow dynamically consumes a lot of resources. For small arrays with 100 elements, the costs are not severe, but for larger arrays the exponentially growing effort is a DON'T for efficient code. But at least, it works:

A = zeros(0, 2);
for k = 1:1000;
    StepNumber = randi(10);
    m = find(A(:, 1) == StepNumber);
    if isempty(m)               % StepNumber not in the list yet
        A(end+1, :) = [StepNumber, 1];
    else
        A(m, 2) = A(m, 2) + 1;  % E.g. increase the counter
    end
end

Of course this example could be implemented more efficiently, e.g.:

A = zeros(10, 2);
for k = 1:1000;
    StepNumber = randi(10);
    A(StepNumber, 2) = A(StepNumber, 2) + 1;  % E.g. increase the counter
end

This avoids the growing of the array and searching in the list of formerly defined StepNumbers.