Metadata may not be needed

[AlenkaF]

Check if the use of metadata is not necessary

It is possible to use the info of categories from the columns like this:

self._col.df.some_function()

without needing to specify the metadada.

[AlenkaF]

The metadata for categories is not needed. I deleted all usage of it and used self._col.df.some_function() to retrieve the info about categorical columns.

See research Notebook.

What needed to be done also is to separately define the dtype for categorical columns (in Vaex dtype of a categorical column is the dtype of data itself). I am not sure if the default is correct:

(_DtypeKind.CATEGORICAL, 64, 'u', '=')

vaex-df-api-implementation/notebook_research/vaex_implementation_v11.py

Lines 288 to 292 in 1002192

	# Categorical
	# If it is internal, kind is categorical (23)
	# If it is external (call from_dataframe) must give data dtype
	if self._col.df.is_category(self._col):
	return (_DtypeKind.CATEGORICAL, 64, 'u', '=') # what should be the default??

[AlenkaF]

Will deal with categorical dtype in #5.