Default value for img_data should contain expected column names #45

nrows = 200
ncols = 500
counts = np.random.rand(nrows, ncols)
tspe = SpatialExperiment(assays={"spots": counts})

tspe.add_img(
    image_source="spatialexperiment/tests/images/sample_image4.png",
    scale_factor=1,
    sample_id="sample_2",
    image_id="unsplash",
)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[6], line 6
      3 counts = np.random.rand(nrows, ncols)
      4 tspe = SpatialExperiment(assays={"spots": counts})
----> 6 tspe.add_img(
      7     image_source="spatialexperiment[/tests/images/sample_image4.png](http://localhost:8888/tests/images/sample_image4.png)",
      8     scale_factor=1,
      9     sample_id="sample_2",
     10     image_id="unsplash",
     11 )

File [/opt/homebrew/Caskroom/miniforge/base/envs/biocpy/lib/python3.12/site-packages/spatialexperiment/SpatialExperiment.py:868](http://localhost:8888/opt/homebrew/Caskroom/miniforge/base/envs/biocpy/lib/python3.12/site-packages/spatialexperiment/SpatialExperiment.py#line=867), in SpatialExperiment.add_img(self, image_source, scale_factor, sample_id, image_id, load, in_place)
    858     spi = construct_spatial_image_class(image_source, is_url=False)
    860 new_row = BiocFrame(
    861     {
    862         "sample_id": [sample_id],
   (...)
    866     }
    867 )
--> 868 new_img_data = self._img_data.combine_rows(new_row)
    870 output = self._define_output(in_place)
    871 output._img_data = new_img_data

File [/opt/homebrew/Caskroom/miniforge/base/envs/biocpy/lib/python3.12/site-packages/biocframe/BiocFrame.py:1406](http://localhost:8888/opt/homebrew/Caskroom/miniforge/base/envs/biocpy/lib/python3.12/site-packages/biocframe/BiocFrame.py#line=1405), in BiocFrame.combine_rows(self, *other)
   1404 def combine_rows(self, *other):
   1405     """Wrapper around :py:func:`~biocutils.combine_rows`."""
-> 1406     return _combine_rows_bframes(self, *other)

File [/opt/homebrew/Caskroom/miniforge/base/envs/biocpy/lib/python3.12/site-packages/biocframe/BiocFrame.py:1445](http://localhost:8888/opt/homebrew/Caskroom/miniforge/base/envs/biocpy/lib/python3.12/site-packages/biocframe/BiocFrame.py#line=1444), in _combine_rows_bframes(*x)
   1443         has_rownames = True
   1444     if df.shape[1] != first_nc:
-> 1445         raise ValueError(
   1446             "All objects to combine must have the same number of columns (expected "
   1447             + str(first_nc)
   1448             + ", got "
   1449             + str(df.shape[1])
   1450             + ")."
   1451         )
   1453 new_data = {}
   1454 for i, col in enumerate(x[0]._column_names):

ValueError: All objects to combine must have the same number of columns (expected 0, got 4).

from biocframe import BiocFrame
tspe._img_data = BiocFrame(data={"sample_id":[], "image_id":[], "data":[], "scale_factor":[]}, number_of_rows=0, column_names=["sample_id", "image_id", "data", "scale_factor"])
tspe.add_img(
    image_source="spatialexperiment/tests/images/sample_image4.png",
    scale_factor=1,
    sample_id="sample_2",
    image_id="unsplash",
)
print(tspe)