I am trying to convert a numpy array
np.array([1,3,2])
to
np.array([[1,0,0],[0,0,1],[0,1,0]])
Any idea of how to do this efficiently? Thanks!
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4 Answers
Create an bool array, and then fill it:
import numpy as np
a = np.array([1, 2, 3, 0, 3, 2, 1])
b = np.zeros((len(a), a.max() + 1), bool)
b[np.arange(len(a)), a] = 1
1 Comment
Paul Panzer
This should be the fastest for all but the smallest operands.
It is also possible to just select the right values from np.eye or the identity matrix:
a = np.array([1,3,2])
b = np.eye(max(a))[a-1]
This would probably be the most straight forward.
Comments
You can compare to [1, 2, 3] like so:
>>> a = np.array([1,3,2])
>>> np.equal.outer(a, np.arange(1, 4)).view(np.int8)
array([[1, 0, 0],
[0, 0, 1],
[0, 1, 0]], dtype=int8)
or equivalent but slightly faster
>>> (a[:, None] == np.arange(1, 4)).view(np.int8)
Comments
Try pandas's get dummy method.
import pandas as pd
import numpy as np
arr = np.array([1 ,3, 2])
df = pd.get_dummies(arr)
if what you need is numpy array object, do:
arr2 = df.values
