dataframe dereferencing

[CdeMills]

Hello,

Jaroslav pointed me that MatLab disallow accesses with cascaded parenthesis
a = randn(3, 3)
a(1:2, 1:2)(:)

I designed my dataframe objects with the ability to specify an output type
specifier at the end, like
x(1:3, 1:2)(:).cell. This result is different from 
y = x(1:3, 1:2)(:) <= if types are compatible, y is a matrix
z = y.cell <= this results in an error

So I modified the code to accept the following syntax:
x.dataframe; x.df => returns a selection of the dataframe as a dataframe
object
x.cell => returns a selection of a dataframe as a cell array with row and
columns names; this array can be converted back to a dataframe
x.as.something => returns a selection of a dataframe as a matrix of type
something. This permits to extract at once columns of different type,
otherwise the code returns an error. Columns are casted to the type
'something'.
x.as.cell => returns a selection of a dataframe as a cell array without row
and column names
x.attributes => return attributes, valid values are 'rownames', 'colnames',
'rowcnt', 'rowidx', 'colcnt', ...
x.colname => return the column with matching name

With this system:
- chaining rule seems OK to me
- conversion purpose seems more clear

Comment / advices ? Are there standard rules to dereference objects with the
'.' operator ?

Regards

Pascal
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