python - Key error '0' when multiplying by a length 1 pandas series

Question

For reasons, I'm currently running a for loop in which A x N arrays (actually xarray data arrays, but the problem persists with basic numpy arrays as in the MRE below) are multiplied by N x 1 pandas series (to form A x 1 arrays), for various Ns.

This works fine as long as N>1. But as soon as N=1 (aka the entire array is just multiplied by the same value), an odd KeyError appears (see below).

import pandas as pd
import numpy as np

# Size 2x1 series, multiplication works fine
a = np.reshape(np.array(np.random.rand(10,2)),(10,-1))
b = [pd.Series(data=[1.0,1.0],index=[1,2])]
a*b


# Size 1x1 series, multiplication fails 
a = np.reshape(np.array(np.random.rand(10,1)),(10,-1))
b = [pd.Series(data=[1.0],index=[1])]
a*b

# With following error message
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-112-d29b22165258> in <module>
      1 a = np.reshape(np.array(np.random.rand(10,1)),(10,-1))
      2 b = [pd.Series(data=[1.0],index=[1])]
----> 3 a*b

~/opt/anaconda3/envs/climate1/lib/python3.7/site-packages/pandas/core/series.py in __getitem__(self, key)
    869         key = com.apply_if_callable(key, self)
    870         try:
--> 871             result = self.index.get_value(self, key)
    872 
    873             if not is_scalar(result):

~/opt/anaconda3/envs/climate1/lib/python3.7/site-packages/pandas/core/indexes/base.py in get_value(self, series, key)
   4402         k = self._convert_scalar_indexer(k, kind="getitem")
   4403         try:
-> 4404             return self._engine.get_value(s, k, tz=getattr(series.dtype, "tz", None))
   4405         except KeyError as e1:
   4406             if len(self) > 0 and (self.holds_integer() or self.is_boolean()):

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

KeyError: 0

I've found a workaround that replaces explicitly the series with floats:

# This works fine
a = np.reshape(np.array(np.random.rand(10,1)),(10,-1))
b = [pd.Series(data=[1.0],index=[1])]
a*[float(k) for k in b]

But I would love any help in understanding where this error message comes from; since I suspect that I'm misunderstanding something more fundamental about pandas.

Thank you in advance!

Answer 1

等待大神答复