如何从 rust 中的无符号 integer 数组中删除值

Question

I am trying to write a function that removes all occurrences of 1,2 and 3 from an array of unsigned integers. I have used the retain method but the error I am getting is:

rustc -o main main.rs
error[E0599]: no method named `retain` found for array `[u32; 7]` in the current scope
 --> main.rs:3:5
  |
3 | arr.retain(|&x| x != 1 || x != 2 || x != 3);
  |     ^^^^^^ method not found in `[u32; 7]`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0599`.
compiler exit status 1

This is what I have so far:

fn remover(arr:[u32;7]){

arr.retain(|&x| x != 1 || x != 2 || x != 3);
println!("{:?}",arr);

}

fn main() {
    let v = [1,2,3,4,5,6,7];
    remover(v);
    
}

Why can I not use the retain method? Is there something else I can use?

Answer 1

An array has a fixed size ( [u32; 7] will always have 7 elements), therefore it doesn't make sense to remove elements from it.

If you want a dynamically sized sequence, you should use Vec , which does have aretain method .

Or you could keep an array and use Iterator::filter , if you don't actually need to update the source.

Answer 2

Arrays are statically sized in Rust, its size is part of the type. [u32; 7] [u32; 7] defines the array to hold exactly 7 u32 values.

If you want to have a dynamic number of values, you will need to use Vec<u32> instead, ie declare v as vec,[1,2,3,4,5,6,7] and make your remover() take Vec<u32> instead.

Answer 3

An alternative solution, you can proceed to filter to a slice of your array. By doing you do not duplicate data, avoiding creating a new vector.

fn main()
{
    let v = [1,2,3,4,5,6,7];
    let v_filtered = &v
        .iter()
        .filter(|&&x| x != 1 && x != 2 && x != 3)
        .inspect(|&&x| println!("retained {}", x))
        .collect::<Vec<_>>();

    dbg!(v);
    dbg!(v_filtered);
}

Pay attention, I changed the predicate of my filter. Here is my playground

You can remove debugging info and iteration inspection value for the release version.