pd.concat throws a ValueError: all the input array dimensions except for the concatenation axis must match

Question

I've got an error merging two dataframes by row. The last version I used pd.concat([df1, df2], axis=0), but in pandas version 2.1.0 doesn't work. Anybody knows how to solve the error?

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[47], line 2
      1 print(real_last.shape, real_exp.shape) #(59202, 34) (4583, 34)
----> 2 real_out = pd.concat([real_exp, real_last], axis=0)
      3 print(real_out.shape)

File c:\Users\sarud\anaconda3\envs\ETLupdate\Lib\site-packages\pandas\core\reshape\concat.py:393, in concat(objs, axis, join, ignore_index, keys, levels, names, verify_integrity, sort, copy)
    378     copy = False
    380 op = _Concatenator(
    381     objs,
    382     axis=axis,
   (...)
    390     sort=sort,
    391 )
--> 393 return op.get_result()

File c:\Users\sarud\anaconda3\envs\ETLupdate\Lib\site-packages\pandas\core\reshape\concat.py:680, in _Concatenator.get_result(self)
    676             indexers[ax] = obj_labels.get_indexer(new_labels)
    678     mgrs_indexers.append((obj._mgr, indexers))
...
--> 230 return super()._concat_same_type(to_concat, axis=axis)

File arrays.pyx:190, in pandas._libs.arrays.NDArrayBacked._concat_same_type()

ValueError: all the input array dimensions except for the concatenation axis must match exactly, but along dimension 1, the array at index 0 has size 4583 and the array at index 1 has size 59202

I have the packages: print(sys.version, pd.__version__, np.__version__, sep='\n')

3.11.5 | packaged by Anaconda, Inc. | (main, Sep 11 2023, 13:26:23) [MSC v.1916 64 bit (AMD64)]
2.1.0
1.26.0

The dataframes has the same structure, check a sample:

print(real_last.sample(2).T.to_markdown())

	43597	9338
Orden	006710000	006781111
Operacion	0010	0020
Operacion.text	XXXXXX	YYYYYYY
Cl.orden	NP	NP
Cl.actividad	030	035
Ubic.tecnica	XXXX-XX-LAS-DES-BAP19	XXXX-XX-S13-MBA
Status.sistema	CTEC NOTI IMOP KKMP PREC	LIB. IMOP KKMP PREC
Status.sistema.op	NOTI CONT CTEC NLIQ	LIB. NLIQ
Stat.Usuario	TRAT	TRAT
Fe.Entrada	2023-06-25 00:00:00	2023-07-23 00:00:00
Fe.Lib	2023-07-06 00:00:00	2023-07-23 00:00:00
Fe.Ini.real.ot	2023-07-01 00:00:00	NaT
Fe.Ini.real.op	2023-07-01 00:00:00	NaT
Fe.Ini.temp	2023-07-06 00:00:00	2023-07-23 00:00:00
Aviso	00120100	11194911
Modif.por	XXXXX005	XXXXX011
Fe.Modif	2023-07-06 00:00:00	2023-07-23 00:00:00
Autor	XXXXX003	XXXXX021
Grupo.planif	XXT	XX1
G.hojas.ruta	nan	nan
CGH	nan	nan
Plan.mant.prev	nan	nan
Pos.PM	nan	nan
Pto.tbjo.resp	XXXXXXXX	XXXXXXXX
Pto.tbjo.op	XXXXXXXX	XXXXXXXX
Cantidad	1	0
Duracion.normal	1.0	0.0
Trabajo	1.0	0.0
Trabajo.real	1.0	0.0
Costos tot.reales	147.03	0.0
Sum.costo.plan	147.03	479.96
Tot.plan.general	147.03	479.96
Total.real.general	147.03	0.0
Costo.dist	0.0	0.0

print(real_exp.sample(2).T.to_markdown())

	926	990
Orden	222212222	333323333
Operacion	0120	0040
Operacion.text	XXXXXXXXXX	YYYYYYYYY
Cl.orden	PL	PL
Cl.actividad	010	010
Ubic.tecnica	XXXX-XX-S07-ALI-CTR7B	XXXX-XX-SCA-AL2-AOG1C
Status.sistema	CTEC NOTI IMPR FMAT IMOP MOVM NLIQ PREC*	LIB. NOTI IMPR DOCU IMOP KKMP NLIQ PREC*
Status.sistema.op	NOTI CTEC IMPR NLIQ	NOTI CONT IMPR LIB. NLIQ PLAN
Stat.Usuario	TBTR	TRAT
Fe.Entrada	2023-08-02 00:00:00	2023-08-02 00:00:00
Fe.Lib	2023-08-23 00:00:00	2023-08-21 00:00:00
Fe.Ini.real.ot	2023-09-04 00:00:00	2023-09-05 00:00:00
Fe.Ini.real.op	2023-09-05 00:00:00	2023-09-06 00:00:00
Fe.Ini.temp	2023-09-07 00:00:00	2023-09-04 00:00:00
Aviso	33333333	44444444
Modif.por	XXXXX009	XXXXX003
Fe.Modif	2023-09-10 00:00:00	2023-09-07 00:00:00
Autor	XXXXXXXXXXXX	XXXXXXXXXXXX
Grupo.planif	XX0	XXC
G.hojas.ruta	1886	76326
CGH	3	3
Plan.mant.prev	8763	191111
Pos.PM	95475	357140
Pto.tbjo.resp	XXXXXXXX	XXXXXXXX
Pto.tbjo.op	XXXXXXXX	XXXXXXXX
Cantidad	4	2
Duracion.normal	4.0	1.0
Trabajo	16.0	2.0
Trabajo.real	16.0	0.5
Costos tot.reales	1627.5	0.04
Sum.costo.plan	2336.45	0.09
Tot.plan.general	2336.45	0.09
Total.real.general	1627.5	0.04
Costo.dist	nan	nan

Answer 1

I can't trigger the ValueError with the given examples but, since your dataframes hold datetimes values, this could be maybe due to a dtypes and/or resolution mismatch like in this Q/A. You can also check GH55067 that discusses a similar issue.

Try this :

real_out = pd.concat([real_exp, real_last.astype(real_exp.dtypes)], axis=0)

Output :

print(real_out)

           Orden Operacion  ... Total.real.general Costo.dist
926    222212222      0120  ...             1627.5        NaN
990    333323333      0040  ...               0.04        NaN
43597  006710000      0010  ...             147.03        0.0
9338   006781111      0020  ...                0.0        0.0

[4 rows x 34 columns]