MATLAB unable to assign variables to elements of a matrix

Question

I am trying to write a simple implementation of a stack in MATLAB, I have used a piece of code earlier in my work similar to:

A = zeros(5,3)
[x, y] = size(A)

This, as expected assigns x to 5, and y to 3, as desired, however I have tried to do a similar thing in my stack implementation and it's throughing an error:

  function [x, y] = pop(obj)
        [x, y] = obj.Data(1, :);
        obj.Data(1, :) = [];
   end

Error: Indexing cannot yield multiple results.

I tried to first extract the 2x1 matrix and then assign it, but that didn't work either:

    function [x, y] = pop(obj)
        top = obj.Data(1, :);
        [x, y] = top;
        obj.Data(1, :) = [];
    end

Error: Too many output arguments

This seems strange to me and an explanation of why this occurs would be very interesting, as well as a work around for this

Thank you.

What obj is? What is top that comes out? If, as you state, top is a 2x1 matrix, you have to extract the values with x = top(1,1) and y = top (2,1). — marcoresk
– marcoresk, Commented Sep 5, 2017 at 7:52

rahnema1 · Accepted Answer · 2017-09-05 07:55:01Z

2

That is because of that size is a function/operation that can return multiple outputs but indexing operations such as Data(1,:) can only return one output as an array, and an array can not be considered as multiple outputs. You can do the following:

top = num2cell(obj.Data(1, :));
[x, y] = top{:}; %or [x, y] = top{1:2};

Here you converted an array to a cell array and by {:} you created a comma separated list that can be assigned to multiple variables.

Or they can be assigned separately

x = obj.Data(1, 1);
y = obj.Data(1, 2);

answered Sep 5, 2017 at 7:55

rahnema1

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