[FIX] Support Sparse Data in Domain Editor

[nikicc]

Issue

Fixes #2188.

Description of changes

Enhance DomainEditor.get_domain to handle sparse data. Also instead of returning a list of columns' the method itself merges them to appropriate X, y and meta arrays.

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #2245 into master will increase coverage by 0.01%.
The diff coverage is 89.65%.

@@            Coverage Diff             @@
##           master    #2245      +/-   ##
==========================================
+ Coverage   72.37%   72.39%   +0.01%     
==========================================
  Files         319      319              
  Lines       55014    55056      +42     
==========================================
+ Hits        39819    39858      +39     
- Misses      15195    15198       +3

[jerneju]

Can you reduce complexity?

[jerneju]

Traceback (most recent call last):
  File "/home/jernej/Projects/Orange2/orange3/Orange/widgets/data/owfile.py", line 241, in select_file
    self.load_data()
  File "/home/jernej/Projects/Orange2/orange3/Orange/widgets/data/owfile.py", line 322, in load_data
    self.apply_domain_edit()  # sends data
  File "/home/jernej/Projects/Orange2/orange3/Orange/widgets/data/owfile.py", line 404, in apply_domain_edit
    domain, cols = self.domain_editor.get_domain(self.data.domain, self.data)
  File "/home/jernej/Projects/Orange2/orange3/Orange/widgets/utils/domaineditor.py", line 280, in get_domain
    col_data = self._to_column(col_data, is_sparse, dtype=object)
  File "/home/jernej/Projects/Orange2/orange3/Orange/widgets/utils/domaineditor.py", line 213, in _to_column
    raise ValueError('Cannot set dtype on sparse matrix.')
ValueError: Cannot set dtype on sparse matrix.

[jerneju]

Open corpus file, then iris, and then again corpus.

[nikicc]

@jerneju should be fixed now, please check again.

[jerneju]

https://sentry.io/biolab/orange3/issues/283621279/

[jerneju]

https://sentry.io/biolab/orange3/issues/219559886/

[jerneju]

https://sentry.io/biolab/orange3/issues/269413491/