CODEWITHSUNDEEP
rustrust-ndarray
Codey McCodeface
Codey McCodeface

Reputation: 3028

Rust ndarray slicing

I am using ndarray and trying to slice some arrays. This works

    let y = arr2(&[[ 6,  5,  4],
                   [12, 11, 10]]);
    let ip = y.slice(s![0, ..]);
    println!("IP {}", ip);

but this

    let y = arr2(&[[ 6,  5,  4],
                   [12, 11, 10]]);
    let ip = y.slice(s![0, ..]);
    println!("IP {}", ip[0]);

does not compile. What is going on?

Compile errors are:

Error[E0277]: the trait bound `i32: Dimension` is not satisfied 

....

println!("IP {}", ip[0]);
| ^^^^^ the trait `Dimension` is not implemented for `i32`
| = note: required because of the requirements on the impl of `std::ops::Index<i32>` for `ArrayBase<ViewRepr<&i32>, i32>`

with other errors

error[E0308]: mismatched types
....
|         let ip = y.slice(s![0, ..]);
|                  ^^^^^^^^^^^^^^^^^^ expected `i32`, found struct `Dim`
|
= note: expected type `i32`
        found struct `Dim<[usize; 1]>`

Upvotes: 0

Views: 1027

Answers (1)

BallpointBen
BallpointBen

Reputation: 13790

The issue is that integer literals are by default i32, and so ip[0] tells Rust that ip: Index<i32>, which then fixes the type of slice's argument to be i32, but the type is supposed to be impl Dimension. (I don't fully understand the type hierarchy of ndarray's indices/dimensions, but this is close enough to be useful.) To work around this, simple replace ip[0] with ip[0_usize].

Upvotes: 0

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