Set all values between 2 ranges in numpy array to certain value

Question

I have 2 1d arrays of type int and a start and a stop value that look like this:

y_start = #some number
y_end = #some number
x_start = #some array of ints
x_end = #some array of ints

What I want is to simulate the following behavior without loops:

for i, y in enumerate(range(y_start, y_end)):
    arr[x_start[i]:x_end[i], y] = c

Example:

y_start = 2
y_end = 5
x_start = np.array([2, 1, 3])
x_end = np.array([4, 3, 6])
c = 1

Input

arr = array([[0, 0, 0, 0, 0, 0, 0],
             [0, 0, 0, 0, 0, 0, 0],
             [0, 0, 0, 0, 0, 0, 0],
             [0, 0, 0, 0, 0, 0, 0],
             [0, 0, 0, 0, 0, 0, 0],
             [0, 0, 0, 0, 0, 0, 0]])

Output:

arr = array([[0, 0, 0, 0, 0, 0, 0],
             [0, 0, 0, 1, 0, 0, 0],
             [0, 0, 1, 1, 0, 0, 0],
             [0, 0, 1, 0, 1, 0, 0],
             [0, 0, 0, 0, 1, 0, 0],
             [0, 0, 0, 0, 1, 0, 0]])

Would this be possible?

what does arr look like? Please provide an explicit complete example (input + output) — mozway
– mozway, Commented Sep 5, 2022 at 18:01
This is for triangle rasterization so arr is pretty big but ill put smaller example. — Aayush
– Aayush, Commented Sep 5, 2022 at 18:04
Yes, please use a minimal example (also provide the start/end values and the output) — mozway
– mozway, Commented Sep 5, 2022 at 18:07

mozway · Accepted Answer · 2022-09-05 18:38:25Z

4

You can use indexing and a crafted boolean arrays converted to integer:

v = np.arange(arr.shape[0])[:,None]
                                                  # conversion to int is implicit
arr[:, y_start:y_end] = ((v>=x_start) & (v<x_end))#.astype(int)

output:

array([[0, 0, 0, 0, 0, 0, 0],
       [0, 0, 0, 1, 0, 0, 0],
       [0, 0, 1, 1, 0, 0, 0],
       [0, 0, 1, 0, 1, 0, 0],
       [0, 0, 0, 0, 1, 0, 0],
       [0, 0, 0, 0, 1, 0, 0]])

answered Sep 5, 2022 at 18:38

mozway

267k13 gold badges56 silver badges106 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Set all values between 2 ranges in numpy array to certain value

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related