rot90 function?

[alper]

I'm looking around, but is there really no rot90 function on a square array?

[alper]

I have it like this, but something built-in would be nice:

fn rot90(arr: &Array2<u32>) -> Array2<u32> {
    arr.t().dot(&Array2::eye(arr.nrows()).slice(s![..,..;-1]))
}

[jturner314]

Fwiw, it's possible to implement the default case (2-D, 90 deg counterclockwise) in a somewhat simpler way:

use ndarray::{array, ArrayBase, Axis, Ix2, RawData};

fn rot90<S>(arr: &mut ArrayBase<S, Ix2>)
where
    S: RawData,
{
    arr.swap_axes(0, 1);
    arr.invert_axis(Axis(0));
}

fn main() {
    let mut a = array![[1, 2, 3], [4, 5, 6]];
    println!("before:\n{}", a);
    rot90(&mut a);
    println!("after:\n{}", a);
}

This doesn't copy the data; it just modifies the shape and strides.

(If you don't want to modify the original array, you could clone it before calling rot90, or call rot90 on a view of the array.)

I agree that it would be worthwhile to add an equivalent to NumPy's rot90 (including the optional parameters) just to simplify things for users and help users port code, even though sequences of swap_axes and invert_axis can accomplish the same thing for specific values of the optional parameters.

Would someone be interested in implementing an equivalent to NumPy's rot90 function?

[alper]

Thanks, because the function signature I have there does not work and I have no clue to fix it when I get an error message (forthcoming, from the other laptop).