BUG: Panel does not preserve DataFrame dtypes

[jzwinck]

A small, complete example of the issue

>>> df = pd.DataFrame({'a':[1,2,3], 'b':[True,False,True]})
>>> df.dtypes
a    int64
b     bool
dtype: object

>>> pl = pd.Panel({'x':df})
>>> pl.x.dtypes
a    object
b    object
dtype: object

Expected Output

I expected the dtypes of df and pl.x to match, the latter was created directly from the former.

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 3.13.0-85-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.1

[jorisvandenbossche]

See the docs here: http://pandas.pydata.org/pandas-docs/stable/dsintro.html#from-dict-of-dataframe-objects:

Orient is especially useful for mixed-type DataFrames. If you pass a dict of DataFrame objects with mixed-type columns, all of the data will get upcasted to dtype=object unless you pass orient='minor':

So

In [38]: pl = pd.Panel.from_dict({'x':df}, orient='minor')

In [39]: pl
Out[39]: 
<class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 3 (major_axis) x 1 (minor_axis)
Items axis: a to b
Major_axis axis: 0 to 2
Minor_axis axis: x to x

In [41]: pl.dtypes
Out[41]: 
a    int64
b     bool
dtype: object

But note what @shoyer said in the other issue, we are planning to deprecate Panels: #13563

[jzwinck]

OK, thanks. If Panel weren't being deprecated I would suggest making this "just work" by default.

[jorisvandenbossche]

Note that there is no "just work", as using orient='minor' gives you a different data structure (the axes are different), so it's not a drop in replacement with better dtype handling.