I have three series. I need to do the following operation element-wise:

1. Compare values from the first and second series.
2. If first is larger take arc-sinus of the element from the third series.
3. Otherwise take arc-cosine.

This is what I managed to do so far:

```
numpy.if(numpy.less(s1,s2),numpy.arcsin(s3),numpy.arccos(s3))

```

Unfortunately if does not work because `numpy.if` does not exist. Is there a way to overcome this problem?