CODEWITHSUNDEEP
pythonnumpy
Andrew Fells
Andrew Fells

Reputation: 89

Finding the slices from a list of coordinates in a numpy

I want to retrieve a list of slices from a list of coordinates in a multidimensional numpy.

What I am doing is the following (example).

First, I declare my base array:

base = np.zeros((8, 8, 4))

with a list of coordinates:

coord = [slice(0, 1, None), slice(0, None, None)]

Second, I create a "mask" in the numpy:

base[coord] = -1

Then, I extract the slices of that area:

np.argwhere(base == -1)

The problem I have is that I don't want to modificate the numpy in order to extract the coordinates, and of course a copy is not a possible solution. What's the way to do it or what modification I should do for obtaining the slices?

Upvotes: 0

Views: 374

Answers (2)

javidcf
javidcf

Reputation: 59731

You can create the array of coordinates with np.meshgrid, using ranges instead of slices:

import numpy as np

base = np.zeros((8, 8, 4))
coord = [range(0, 1), range(0, base.shape[1])]
coords_array = np.stack(np.meshgrid(*coord, indexing='ij'), -1).reshape(-1, len(coord))
print(coords_array)
# [[0 0]
#  [0 1]
#  [0 2]
#  [0 3]
#  [0 4]
#  [0 5]
#  [0 6]
#  [0 7]]

Upvotes: 2

Sayandip Dutta
Sayandip Dutta

Reputation: 15872

Try this:

import numpy as np
base = np.zeros((8, 8, 4))
coord = [slice(0, 1, None), slice(0, None, None)]
all_coords = np.argwhere(base == base).reshape(*base.shape,base.ndim)  # (8,8,4,3)
print(all_coords[coord].reshape(-1,base.ndim))

Output:

[[0 0 0]
 [0 0 1]
 [0 0 2]
 [0 0 3]
 [0 1 0]
 [0 1 1]
 [0 1 2]
 [0 1 3]
 [0 2 0]
 [0 2 1]
 [0 2 2]
 [0 2 3]
 [0 3 0]
 [0 3 1]
 [0 3 2]
 [0 3 3]
 [0 4 0]
 [0 4 1]
 [0 4 2]
 [0 4 3]
 [0 5 0]
 [0 5 1]
 [0 5 2]
 [0 5 3]
 [0 6 0]
 [0 6 1]
 [0 6 2]
 [0 6 3]
 [0 7 0]
 [0 7 1]
 [0 7 2]
 [0 7 3]]

Upvotes: 1

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