How to own a part of array, just like what OpenCV does?

[fzyzcjy]

Hi thanks for the lib! I want to own a part of array, just like what OpenCV does. Consider the (simplified) code:

fn read_and_crop_image() -> ??? {
  let big_image: Array2<u8> = read_the_image();
  let cropped = big_image.slice(s![0..3000, 0..4000]);
  cropped // ERROR!!
}

However it errors, since ArrayView should not outlive the Array it belongs to. I have tried ArcArray but it does not seem to support .slice() as well.

With OpenCV I can do:

fn read_and_crop_image() -> Mat {
  let big_image: Mat = read_the_image();
  let cropped = Mat::roi([0..3000, 0..4000], big_image);
  cropped // no problem, it is another Mat, and underlying it is reference counting
}

[jturner314]

You could use .slice_move(), .slice_collapse(), or other similar methods, and return an owned Array2<u8>, e.g.:

fn read_and_crop_image() -> Array2<u8> {
    let big_image: Array2<u8> = read_the_image();
    let cropped = big_image.slice_move(s![0..3000, 0..4000]);
    cropped
}

You could also do something similar with ArcArray. The key is to return an owned array type (Array or ArcArray), rather than a view of an array which will be dropped at the end of the function body.

Another option is to copy the relevant portion, which may be beneficial if the original image is much larger than the cropped portion:

fn read_and_crop_image() -> Array2<u8> {
    let big_image: Array2<u8> = read_the_image();
    let cropped = big_image.slice(s![0..3000, 0..4000]).to_owned();
    cropped
}

[fzyzcjy]

Thank you!