CODEWITHSUNDEEP
pythonarraysnumpy
MRocklin
MRocklin

Reputation: 57271

Use NumPy to index one array with another

Given some data

In [1]: import numpy as np
In [2]: x = np.array(['a', 'b', 'b', 'a'])

And a sorted index

In [3]: i = np.array(['a', 'b'])

I want to find the location of each data entry within the index

In [4]: # solution here
array([0, 1, 1, 0])

This is a bit like categoricals. I don't want to use Pandas here. I want to do this on fixed length strings. I need this to be somewhat efficient.

Upvotes: 2

Views: 83

Answers (1)

Alex Riley
Alex Riley

Reputation: 176750

You could use np.searchsorted:

>>> np.searchsorted(i, x)
array([0, 1, 1, 0])

The function finds out the index at which each element of x should be placed in i in order to maintain sorted order.

Upvotes: 5

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