to_sparse and assign is giving the wrong results.

[wellimbharath]

Coming from SO, when a boolean scalar is assigned to a new column using assign, it is leading to wrong results. Why is that so?

df = pd.DataFrame({"a":[1,2,3]}).to_sparse(fill_value=False)
df.assign(newcol=False)

   a  newcol
0  1     0.0
1  2     0.0
2  3     0.0

This works as expected if the dataframe is dense i.e

df.to_dense().assign(newcol=False).to_sparse()

   a  newcol
0  1   False
1  2   False
2  3   False

Is this a bug or is this a genuine thing that's happening?

[jreback]

xref to #18924

This is quite tricky actually; you are starting with a SparseDataFrame which has some special properties; .assign() should convert this to a DataFrame.

So this is currently not supported.

cc @hexgnu

[hexgnu]

Just put together a quick bug fix for this.