How can I update a mutable slice?

help
1

Hi All,
I am facing an error while using slice. Is it possible to modify a slice?

fn test(my_slice: &mut [f32]) {
    let my_local = vec![3f32; my_slice.len()];
    *my_slice = my_slice.iter().zip(my_local).map(|(a,b)| a + b).collect();
}
fn main() {
    let mut my_vec = vec![5f32; 30];
    test(&mut my_vec.as_slice());
}

I am getting below error,

a value of type &mut [f32] cannot be built from an iterator over elements of type f32

So I added,

*my_slice = &mut my_slice.iter().zip(my_local).map(|(a,b)| a + b).collect();

Then I got below error,

a value of type [f32] cannot be built from an iterator over elements of type f32

2

You can collect into many types, but slice is not one of them. How about modifying the slice directly?

fn test(my_slice: &mut [f32]) {
    let my_local = vec![3f32; my_slice.len()];
    for (a, b) in my_slice.iter_mut().zip(my_local) {
        *a += b;
    }
}
fn main() {
    let mut my_vec = vec![5f32; 30];
    test(&mut my_vec);
}
1 Like
3

Thanks I was thinking passing a vec is not as efficient as slice. One more question - Is it possible to use par_iter() in the for loop? When I use that I am getting an error

the trait `std::iter::Iterator` is not implemented for `rayon::iter::zip::Zip<rayon::slice::IterMut<'_, f32>, rayon::slice::IterMut<'_, f32>>`
4

Well, test will receive a slice anyway - a reference to vector can coerce to it.

1 Like
5

par_iter() does not implement Iterator, but does share a lot of its methods. Something like this might work:

fn test(my_slice: &mut [f32]) {
    let my_local = vec![3f32; my_slice.len()];
    my_slice.par_iter_mut().zip(my_local).for_each(|(a, b)| *a += b);
}
2 Likes
6

Thanks @tuffy. I am following your method now

7

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