Passing from Python to MATLAB a cell array of structures

Let's say that we want to pass from Python an object corresponding to a mixed MATLAB cell array of structures, as an example a final MATLAB object like: toto{1}.weapon{2}.Name='fleurs' ...

I tried in Python:

    >>> import scipy.io as sio
    >>> import numpy as np

    >>> toto = np.zeros((2,), dtype=np.object)
    >>> toto[0] = {}
    >>> toto[1] = {}
    >>> toto[0]['weapon'] = np.zeros((2,), dtype=np.object)
    >>> toto[0]['weapon'][0] = {}
    >>> toto[0]['weapon'][1] = {}
    >>> toto[0]['weapon'][1]['Name'] = 'fleurs'
    >>> toto
array([{'weapon': array([{}, {'Name': 'fleurs'}], dtype=object)}, {}], dtype=object)
    >>> sio.savemat('toto.mat', {'toto':toto})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio.py", line 207, in savemat
    MW.put_variables(mdict)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 876, in put_variables
    self._matrix_writer.write_top(var, asbytes(name), is_global)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 626, in write_top
    self.write(arr)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 655, in write
    self.write_cells(narr)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 759, in write_cells
    self.write(el)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 653, in write
    self.write_struct(narr)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 764, in write_struct
    self._write_items(arr)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 782, in _write_items
    self.write(el[f])
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 655, in write
    self.write_cells(narr)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 759, in write_cells
    self.write(el)
  File "/usr/lib64/python2.7/site-packages/scipy/io/matlab/mio5.py", line 647, in write
    % (arr, type(arr)))
TypeError: Could not convert {} (type <type 'dict'>) to array

So, is it possible to create in Python and pass to MATLAB a cell array of structures ?

Did I make a mistake ?

Answer 1

[Eric Condamine]

Ooops I just understood why the TypeError exception was raised ... In fact, this is the right way to pass a cell array of structures from Python to MATLAB but ... It seems that the scipy.io.savemat does not allow empty dictionary. Indeed If I complet all the dictionnaries all is working fine !:

In Python:

>>> import scipy.io as sio   
>>> import numpy as np

>>> toto = np.zeros((2,), dtype=np.object)
>>> toto[0]={}
>>> toto[1]={}
>>> toto[1]['Site']=['Tataouine']
>>> toto[0]['weapon'] = np.zeros((2,), dtype=np.object)
>>> toto[0]['weapon'][0]={}
>>> toto[0]['weapon'][1]={}
>>> toto[0]['weapon'][1]['Name']='fleurs'
>>> toto[0]['weapon'][0]['Name']='bonbons'
>>> toto
array([ {'weapon': array([{'Name': 'bonbons'}, {'Name': 'fleurs'}], dtype=object)},
       {'Site': ['Tataouine']}], dtype=object)
>>> sio.savemat('toto.mat', {'toto':toto})

In MATLAB:

>> load('toto')
>> toto

toto = 

      [1x1 struct]    [1x1 struct]

>> toto{1}.weapon{2}.Name

ans =

fleurs

Hope this will help you to not waste your time with this silly problem !!

[Ryland Mathews]

I am currently pulling in a pandas dataframe (of strings) into matlab using code like below:

is there a way to then convert the dataframe into usuable form to plot in a matlab table, I tried for hours to convert it and couldnt get it done.

clear classes
mod = py.importlib.import_module('test')
py.importlib.reload(mod)
cP = py.list(py.test.FlowTracker().todays_portfolio(1,10))