concat doesn't work with mixed Series/DataFrames

[dhirschfeld]

concat thows an AssertionError when passed a ciollection of mixed Series and Dataframes e.g.

s1 = pd.TimeSeries(np.sin(linspace(0, 2*pi, 100)), 
                   index=pd.date_range('01-Jan-2013', 
periods=100, freq='H')) 

s2 = pd.TimeSeries(np.cos(linspace(0, 2*pi, 100)), 
                  index=pd.date_range('01-Jan-2013', 
periods=100, freq='H')) 

df = pd.DataFrame(np.cos(linspace(0, 2*pi, 
100)).reshape(-1,1), 
                   index=pd.date_range('01-Jan-2013', 
periods=100, freq='H')) 

In [23]: pd.concat([df,df], axis=1).shape 
Out[23]: (100, 2) 

In [24]: pd.concat([s1,s2], axis=1).shape 
Out[24]: (100, 2) 

In [25]: pd.concat([s1,s2,s1], axis=1).shape 
Out[25]: (100, 3) 

In [26]: pd.concat([s1,df,s2], axis=1).shape 
Traceback (most recent call last):

  File "<ipython-input-9-4512588e71f2>", line 1, in <module>
    pd.concat([s1,df,s2], axis=1).shape

  File "c:\dev\code\pandas\pandas\tools\merge.py", line 881, in concat
    return op.get_result()

  File "c:\dev\code\pandas\pandas\tools\merge.py", line 960, in get_result
    columns=self.new_axes[1])

  File "c:\dev\code\pandas\pandas\core\frame.py", line 376, in __init__
    mgr = self._init_dict(data, index, columns, dtype=dtype)

  File "c:\dev\code\pandas\pandas\core\frame.py", line 505, in _init_dict
    dtype=dtype)

  File "c:\dev\code\pandas\pandas\core\frame.py", line 5181, in _arrays_to_mgr
    mgr = BlockManager(blocks, axes)

  File "c:\dev\code\pandas\pandas\core\internals.py", line 499, in __init__
    self._verify_integrity()

  File "c:\dev\code\pandas\pandas\core\internals.py", line 584, in _verify_integrity
    raise AssertionError('Block shape incompatible with manager')

AssertionError: Block shape incompatible with manager

In [27]: pd.__version__
Out[27]: '0.10.0.dev-fbd77d5'

[wesm]

Well that's not very helpful. Should be improved at some point

[hayd]

Am I right in saying these give better errors in dev?

pd.concat([s1,df,s2])
ValueError: arrays must have same number of dimensions

pd.concat([s1,df,s2], axis=1)
ValueError: Shape of passed values is (3,), indices imply (3, 100)

[jreback]

I like the first one, prob should catch the error in concat and put up a better message for the 2nd one though....

[hayd]

Agreed.

[jreback]

ok...let's move to 0.12 then...

[dhirschfeld]

It's not the incorrect error which is the problem, but the fact that an error is thrown at all. This makes it difficult/tedious to write generic code that works whether or not the input is a DataFrame or a TimeSeries.

In this case the TimeSeries should be treated as a DataFrame with one column where the column label is taken from the TimeSeries name. It the axis parameter was 0 then the TimeSeries should be treated as a DataFrame with one row where the row label is taken from the TimeSeries name.

[jreback]

@dhirschfeld I think we will have a detailed look at this, but nothing is stopping you from pre-conditining, e.g.

 pd.concat([ pd.DataFrame(x) for x in [s1,df,s2] ], axis=1).shape

The DataFrame constructor does exactly what you want for a series with axis=1, and passed thru a DataFrame
(axis=0 you would need to pass the orient so it transposes I think)

[jorisvandenbossche]

I also stumbled on this, but I saw there is already this issue for it.

I think in current master it is still very confusing. An example (with the series being a column from a dataframe, full example: http://nbviewer.ipython.org/5868420/bug_pandas-concat-series.ipynb ):

• concat with [df1, df2[col]]: IndexError: list index out of range
• concat with [df1[col], df2]: AttributeError: 'DataFrame' object has no attribute 'name'

I think at the moment it is not clear from the docs that this is not allowed (mixing dataframes with series/columns), and when you do it, you don't get a very informative error message.

[hayd]

So should work like this:

In [1]: df = pd.DataFrame([[1, 2], [3, 4]])

In [2]: s = pd.Series([5, 6], name=3)

In [3]: pd.concat([df, pd.DataFrame(s).T])  # but with [df, s]
Out[3]:
   0  1
0  1  2
1  3  4
3  5  6

In [4]: pd.concat([df, pd.DataFrame(s)], axis=1)  # but with [df. s]
Out[4]:
   0  1  3
0  1  2  5
1  3  4  6

# also both with [s, df]

[jreback]

series must have a name FYI (otherwise needs to raise)

[hayd]

atm it's a bit sketchy with name:

In [5]: s1 = pd.Series([5, 6])

In [6]: pd.concat([s, s1], axis=1)   # loses name of s
Out[6]:
   0  1
0  5  5
1  6  6

Not sure should always raise w/o name.

[jreback]

@hayd that's the problem, it "works" but really should not (as its assigned as if the column index doesn't exist). I would just be careful about it, maybe only allowing it if as_index=False or series has a name

[jtratner]

not exactly the same situation, but append raises if the appended series doesn't have a name and axis=0, so certainly precedent for it.