Finding first instance of one list in a second list

Question

I have two lists. The first list is already sorted (by some other criteria) such that the earlier in the list, the better. ``` sortedList = ['200', '050', '202', '203', '206', '205', '049', '047', '042', '041', '043', '044', '046', '045', '210', '211', '306', '302', '308', '309', '311', '310', '221', '220', '213', '212'] ``` The second list is a list of allowed values: ``` allowedList = ['001','002','003','004','005','006','007','008','009','010','203','204','205','206','207','212','213','215','216'] ``` I would like to select the highest sorted value that exists in the allowedList, and I'm only coming up with silly ways of doing this. Things like this: ``` import numpy as np temp = [] for x in allowedList: temp.append(sortedList.index(x)) np.min(temp) ``` There has to be a better way than this. Any ideas?

Accepted Answer

The solutions using the fact that `allowedlist` is already sorted are probably more efficient (and using a `set`, they certainly are - linear time vs quadratic), but for completeness only, your existing solution can be shortened a lot and the temporary list eliminated:

```
min(allowedList, key=sortedList.index)
```

This uses Python's built-in `min` function, rather than the one from numpy - `np.min` is mainly only useful if you're using them with numpy arrays; there is no need for it when using lists.

Finding first instance of one list in a second list

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