Re: Cell append -empty element problem (3.6)

[Ben Abbott]

On Dec 13, 2012, at 8:40 AM, octaveuser001 wrote:

> In Octave 3.2.4 when we do
> aa=[];
> bb=cell(2,1);
> bb(1)=char('hello');
> aa=[aa;bb(1)];
> 
> then the value for aa is
> aa =
> {
>  [1,1] = hello
> }
> 
> However with Octave 3.6.2 (windows/Visual studio 2010 Setup/Michael
> Goffioul) the returned value for aa is
> aa =
> {
>  [1,1] = [](0x0)
>  [2,1] = hello
> }
> 
> I recently moved to 3.6 and the empty element is breaking lot of my code.
> Which is the expected correct output?

First using your example, Matlab produces ...

        aa = [];
        bb = cell (2, 1);
        bb(1) = char ('hello');
        Conversion to cell from char is not possible.

Modifying the syntax, and removing some of the semicolons for clarity ...

        aa = [];
        bb = cell (2, 1)

        bb = 

            []
            []

        bb(1) = {'hello'}

        bb = 

            'hello'
            []

        aa = [aa; bb(1)]

        aa = 

            'hello'

Notice that Matlab has dropped the contents of aa.

Octave's result does not drop the aa.

        aa = [];
        bb = cell (2, 1)
        bb = 
        {
          [1,1] = [](0x0)
          [2,1] = [](0x0)
        }

        bb(1) = 'hello'
        bb = 
        {
          [1,1] = hello
          [2,1] = [](0x0)
        }

        aa = [aa; bb(1)]
        aa = 
        {
          [1,1] = [](0x0)
          [2,1] = hello
        }

Now using a simpler example: First with Matlab ...

        [{'foo'}, '', 'bar']

        ans = 

            'foo'    'bar'

and now with Octave ...

        [{'foo'}, '', 'bar']
        ans = 
        {
          [1,1] = foo
          [1,2] = 
          [1,3] = bar
        }

Matlab does not treat all strings equally.  It converted 'bar" to a cell 
string, but dropped the empty string.  I would expect that [{'foo'}, '', 'bar'] 
to be equivalent to  [{'foo'}, {''}, {'bar'}].

Also it also looks inconsistent to me that ...

        bb = [{}, 'hello'];

... produces a cell-string, but using the equivalent syntax below, Matlab 
throws an error .

        bb = cell (1);
        bb(1) = 'hello';
        Conversion to cell from char is not possible.

I assume this was a bug at some point, but may now be supported by Matlab for 
legacy reasons.  This *feature* caused me some frustration in understanding how 
cells worked in Matlab.  For its consistency, I prefer the Octave 
implementation.

Ben