pd.concat(objs, axis=0, join='outer', join_axes=None, ignore_index=False,
keys=None, levels=None, names=None, verify_integrity=False)
result = pd.concat([df1, df4], axis=1)
result = pd.concat(frames, keys=['x', 'y', 'z'])
result = pd.concat([df1, df4], axis=1, join='inner')
result = pd.concat([df1, df4], axis=1, join_axes=[df1.index])