scipy.io.loadmat nested structures (i.e. dictionaries)

Question

Using the given routines (how to load Matlab .mat files with scipy), I could not access deeper nested structures to recover them into dictionaries

To present the problem I run into in more detail, I give the following toy example:

load scipy.io as spio a = {'b':{'c':{'d': 3}}} # my dictionary: a['b']['c']['d'] = 3 spio.savemat('xy.mat',a) 

Now I want to read the mat-File back into python. I tried the following:

vig=spio.loadmat('xy.mat',squeeze_me=True) 

If I now want to access the fields I get:

>> vig['b'] array(((array(3),),), dtype=[('c', '|O8')]) >> vig['b']['c'] array(array((3,), dtype=[('d', '|O8')]), dtype=object) >> vig['b']['c']['d'] --------------------------------------------------------------------------- ValueError                                Traceback (most recent call last)  /<ipython console> in <module>()  ValueError: field named d not found. 

However, by using the option struct_as_record=False the field could be accessed:

v=spio.loadmat('xy.mat',squeeze_me=True,struct_as_record=False) 

Now it was possible to access it by

>> v['b'].c.d array(3) 

Answer 1

Here are the functions, which reconstructs the dictionaries just use this loadmat instead of scipy.io's loadmat:

import scipy.io as spio  def loadmat(filename):     '''     this function should be called instead of direct spio.loadmat     as it cures the problem of not properly recovering python dictionaries     from mat files. It calls the function check keys to cure all entries     which are still mat-objects     '''     data = spio.loadmat(filename, struct_as_record=False, squeeze_me=True)     return _check_keys(data)  def _check_keys(dict):     '''     checks if entries in dictionary are mat-objects. If yes     todict is called to change them to nested dictionaries     '''     for key in dict:         if isinstance(dict[key], spio.matlab.mio5_params.mat_struct):             dict[key] = _todict(dict[key])     return dict          def _todict(matobj):     '''     A recursive function which constructs from matobjects nested dictionaries     '''     dict = {}     for strg in matobj._fieldnames:         elem = matobj.__dict__[strg]         if isinstance(elem, spio.matlab.mio5_params.mat_struct):             dict[strg] = _todict(elem)         else:             dict[strg] = elem     return dict 

Answer 2

Just an enhancement to mergen's answer, which unfortunately will stop recursing if it reaches a cell array of objects. The following version will make lists of them instead, and continuing the recursion into the cell array elements if possible.

import scipy.io as spio import numpy as np   def loadmat(filename):     '''     this function should be called instead of direct spio.loadmat     as it cures the problem of not properly recovering python dictionaries     from mat files. It calls the function check keys to cure all entries     which are still mat-objects     '''     def _check_keys(d):         '''         checks if entries in dictionary are mat-objects. If yes         todict is called to change them to nested dictionaries         '''         for key in d:             if isinstance(d[key], spio.matlab.mio5_params.mat_struct):                 d[key] = _todict(d[key])         return d      def _todict(matobj):         '''         A recursive function which constructs from matobjects nested dictionaries         '''         d = {}         for strg in matobj._fieldnames:             elem = matobj.__dict__[strg]             if isinstance(elem, spio.matlab.mio5_params.mat_struct):                 d[strg] = _todict(elem)             elif isinstance(elem, np.ndarray):                 d[strg] = _tolist(elem)             else:                 d[strg] = elem         return d      def _tolist(ndarray):         '''         A recursive function which constructs lists from cellarrays         (which are loaded as numpy ndarrays), recursing into the elements         if they contain matobjects.         '''         elem_list = []         for sub_elem in ndarray:             if isinstance(sub_elem, spio.matlab.mio5_params.mat_struct):                 elem_list.append(_todict(sub_elem))             elif isinstance(sub_elem, np.ndarray):                 elem_list.append(_tolist(sub_elem))             else:                 elem_list.append(sub_elem)         return elem_list     data = spio.loadmat(filename, struct_as_record=False, squeeze_me=True)     return _check_keys(data)