SUNDONG - 11 months ago 49

Python Question

I want to make a subseries by values when the Series consists of ndarrays.

This one works.

`sa = pd.Series([1,2,35,2],index=list('abcd'))`

sa[sa==2]

Results

`b 2`

d 2

dtype: int64

Why below codes does not work? What should I change?. It gives a ValueError: Lengths must match to compare

`sa2 = pd.Series([np.array(['out']), np.array(['2f-right', '2f']), np.array(['out', '2f']), np.array(['out'])], index=list('abcd'))`

ar = np.array(['out'])

sa2[sa2 == ar]

Answer Source

The comparison operator doesn't understand how to compare for equality with np arrays here so you can use `apply`

with a `lambda`

:

```
In [211]:
sa2[sa2.apply(lambda x: (x == ar).all())]
Out[211]:
a [out]
d [out]
dtype: object
```

So here we compare against the array and use `all`

to generate a boolean mask