Comparing non equal dimension data in pandas

Question

I am looking to compare 2 Series in Pandas. I have the following code

a = pd.Series([1, 2, 3, 4], index = [1, 2, 3, 4])
b = pd.Series([1, 1, 1], index = [1, 5, 4])
a[~a.eq(b)]

In the case when the Series is empty, ie, no values have been added to it as yet.

b = pd.Series()
a[~a.eq(b)]

Both cases give me the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Anaconda3\lib\site-packages\pandas\core\ops.py", line 735, in wrapper
    raise ValueError('Series lengths must match to compare')
ValueError: Series lengths must match to compare

The value I am looking to arrive at is:

2   2
3   3
4   4

in the 1st case and the following in the latter case:

1    1
2    2
3    3
4    4

Answer 1

I think you need Series.reindex for same indices:

print (b.reindex(a.index))
1    1.0
2    NaN
3    NaN
4    1.0
dtype: float64

print (a[~a.eq(b.reindex(a.index))])
2    2
3    3
4    4
dtype: int64

---

print (a[~a.eq(b.reindex(pd.Series([]).index))])
1    1
2    2
3    3
4    4
dtype: int64