subsref works as not expected

Hello!

Let's create random cell array.

test = {1,2,3,4};

And try to evaluate simple code

res_1 = ones(subsref(test, substruct('{}', {':',':'})));
res_2 = ones(test{:, :});

Results unmatch but it should to match according with subsref help. Why?

Is there any way to unpack cell array without direct access through {:}?

Answer 1

[Bruno Luong]

I knew it for sometime: subsref never work to emulate comma list (not sure if it's documented), because a non trivial comma list (with length > 1) can never be considered as function output .

This limitation surely deserves to be in "what frustrates you ..." thread.

[Sergey Kasyanov]

Thanks!

Do you know any way to use {:} with function output?

I mean that way:

res_1 = ones(some_function(var_1, var_2){:})

[Bruno Luong]

First MATLAB won't allow such cascade syntax (this deserves to be "what frustrates you ..." thread as well)

some_function(var_1, var_2){:}

Example:

>> num2cell(1:3)

ans =

  1×3 cell array

    {[1]}    {[2]}    {[3]}

>> num2cell(1:3){:}
Error: Indexing with parentheses '()' must appear as the last operation of a valid indexing expression.
 

The best you can do is this

A = rand(3,4,5)
idx = some_function(1:2,3:4,':');
B = A(idx{:})

function c = some_function (varargin)
c = varargin;
end

But then the function some_function is not useful in any way. Just work directly with cell and comma list will do the same job:

A = rand(3,4,5)
idx = {1:2,3:4,':'};
B = A(idx{:})

[Sergey Kasyanov]

Thanks!