Best way to assign by element when using a generic array

[daniellga]

Hi! In the example below, function load2 works while in load the compiler complains:

error[E0594]: cannot assign to data in an index of `ArrayBase<S, Dim<[usize; 2]>>`
  --> src/lib.rs:25:13
   |
25 |             arr[[idx1, idx2]] = *elem;
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ cannot assign
   |
   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `ArrayBase<S, Dim<[usize; 2]>>`

What would be an efficient and correct way to fill the array in load's case?

use ndarray::{ArrayBase, Ix2, Data, DataOwned, OwnedRepr}; // 0.15.6
use num_traits::Float; // 0.2.15


struct TestStruct<T: Float, S: Data<Elem = T>> {
    data: ArrayBase<S, Ix2>,
}

impl<T, S> TestStruct<T, S>
where
    T: Float,
    S: Data<Elem = T>,
{
    fn load(v: Vec<T>) -> TestStruct<T, S> 
    where
        S: DataOwned,
    {
        let nrows = 3;
        let ncols = 100;
        let mut arr = ArrayBase::<S, Ix2>::zeros((nrows, ncols));
        
        let mut idx1;
        let mut idx2 = 0;
        for (n, elem) in v.iter().enumerate() {
            idx1 = n % 3;
            arr[[idx1, idx2]] = *elem;
            if idx1 == nrows-1 {
                idx2 += 1;
            }
        }
        
        TestStruct { data: arr }
    }
}

impl<T> TestStruct<T, OwnedRepr<T>>
where
    T: Float,
{
    fn load2(v: Vec<T>) -> TestStruct<T, OwnedRepr<T>> 
    {
        let nrows = 3;
        let ncols = 100;
        let mut arr = ArrayBase::<OwnedRepr<T>, Ix2>::zeros((nrows, ncols));
        
        let mut idx1;
        let mut idx2 = 0;
        for (n, elem) in v.iter().enumerate() {
            idx1 = n % 3;
            arr[[idx1, idx2]] = *elem;
            if idx1 == nrows-1 {
                idx2 += 1;
            }
        }
        
        TestStruct { data: arr }
    }
}