Is there a way to fold with index in Rust?

Question

In Ruby, if I had an array a = [1, 2, 3, 4, 5] and I wanted to get the sum of each element times its index I could do

a.each.with_index.inject(0) {|s,(i,j)| s + i*j}

Is there an idiomatic way to do the same thing in Rust? So far, I have

a.into_iter().fold(0, |x, i| x + i)

But that doesn't account for the index, and I can't really figure out a way to get it to account for the index. Is this possible and if so, how?

score 36 · Accepted Answer · answered Dec 11 '16 at 22:10

36

You can chain it with enumerate:

fn main() {
    let a = [1, 2, 3, 4, 5];
    let b = a.into_iter().enumerate().fold(0, |s, (i, j)| s + i * j);

    println!("{:?}", b); // Prints 40
}

answered Dec 11 '16 at 22:10

Simon Whitehead

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Beautiful! That's exactly what I wanted! Thank you. – Eli Sadoff Dec 11 '16 at 22:19
Glad I could help! :) – Simon Whitehead Dec 11 '16 at 22:21
It if use `.enumerate()` to give me the index in a fold, will it add the arguments after the `acc` and `curr` or before ? – duck Jul 16 '17 at 16:02

Is there a way to fold with index in Rust?

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