How to find the x, y coordinate (or index) of values in a 2D array-CodePudding

I have a 2D array I created using this,

import numpy as np

arr = np.arange(4)
arr_2d = arr.reshape(2,2)

The array looks like this

print(arr_2d)
[[0, 1],
 [2, 3]]

I am trying to get the location of each entry in arr_2d as an x, y coordinate, and eventually get an array that looks like this,

print(full_array)
[[0, 0, 0],
[1, 0, 1],
[2, 1, 0],
[3, 1, 1]]

Where the first column contains the values in arr_2d, the second column contains each value's x (or row) coordinate and the third column contains each value's y (or column) coordinate. I tried flattening arr_2d and enumerating to get the index of each entry, but I was unable to get it in this form. Any help will be much appreciated.

CodePudding user response：

Perhaps not the nicest way, but it works (assuming this is what you are after):

import numpy as np

arr = np.arange(4)
arr_2d = arr.reshape(2,2)  

arr_2d[1][0] = 5 # to illustrate a point

print(arr_2d)
dimensions = arr_2d.shape
for y in range(dimensions[0]):
    for x in range(dimensions[1]):
        print(arr_2d[x][y], " (x:", x, " y:", y, ")")

renders:

[[0 1]
 [5 3]]
0  (x: 0  y: 0 )
1  (x: 1  y: 0 )
5  (x: 0  y: 1 )
3  (x: 1  y: 1 )

which you can just put in another array

CodePudding user response：

You can use np.unravel_index():

x = arr_2d.flatten()
r = np.vstack((x,np.unravel_index(np.arange(arr_2d.size),arr_2d.shape))).T

# r = array([[0, 0, 0],
#           [1, 0, 1],
#           [2, 1, 0],
#           [3, 1, 1]], dtype=int64)

Both flatten() and np.unravel_index() use by default a row-major order, so we knows that the right order is preserved.