如何将 integer 添加到 Rust ndarray 的切片中？

Question

Let me try:

let mut a: Array2<usize> = Array2::zeros((20, 20));
let z = a.slice(s![.., 1]);
z += 1;

which gives:

error[E0368]: binary assignment operation `+=` cannot be applied to type `ArrayBase<ViewRepr<&usize>, _>`

Answer 1

If you use u64 instead of usize , you'll succeed. See the following example:

use ndarray::{s, Array2};

pub fn foo() -> Array2<u64> {
    let mut a: Array2<u64> = Array2::zeros((20, 20));
    let z = a.slice(s![.., 1]);
    z += 1;
    z
}

pub fn bar() -> Array2<usize> {
    let mut a: Array2<usize> = Array2::zeros((20, 20));
    let z = a.slice(s![.., 1]);
    z += 1; // NOTE: Fails!
    z
}

Rust playground link of this snippet

It's because ndarray didn't implemented the Add trait for usize type. It's implemented for i32 , u32 , and any other fixed sized integer types though.

References

• https://docs.rs/ndarray/0.12.1/ndarray/struct.ArrayBase.html#impl-Add%3CArrayBase%3CS%2C%20D%3E%3E