CODEWITHSUNDEEP
pythonnumpymatrixscipy
jgilchrist
jgilchrist

Reputation: 43

Array of 1's in indexed positions

I currently have an array of indices of the minimum values in an array.

It looks something like this:

[[0],
 [1],
 [2],
 [1],
 [0]]

(The maximum index is 3)

What I want is an array that looks like this:

[[1, 0, 0]
 [0, 1, 0]
 [0, 0, 1]
 [0, 1, 0]
 [1, 0, 0]]

Where the 1 is in the column of the minimum.

Is there an easy way to do this in numpy?

Upvotes: 3

Views: 71

Answers (2)

roman
roman

Reputation: 117345

for lists you could do

>>> a = [[0], [1], [2], [1], [0]]
>>> N = 3
>>> [[1 if x[0] == i else 0 for i in range(N)] for x in a]
[[1, 0, 0], [0, 1, 0], [0, 0, 1], [0, 1, 0], [1, 0, 0]]

Upvotes: 0

Fred Foo
Fred Foo

Reputation: 363517

Use NumPy's broadcasting of ==:

>>> minima = np.array([[0], [1], [2], [1], [0]])
>>> minima == arange(minima.max() + 1)
array([[ True, False, False],
       [False,  True, False],
       [False, False,  True],
       [False,  True, False],
       [ True, False, False]], dtype=bool)
>>> (minima == arange(minima.max() + 1)).astype(int)
array([[1, 0, 0],
       [0, 1, 0],
       [0, 0, 1],
       [0, 1, 0],
       [1, 0, 0]])

Upvotes: 6

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