如何计算两个 Rust 数组/切片/向量的点积? [英] How do I compute the dot product of two Rust arrays / slices / vectors?

问题描述

我试图找到两个向量的点积:

I'm trying to find the dot product of two vectors:

fn main() {
    let a = vec![1, 2, 3, 4];
    let b = a.clone();
    let r = a.iter().zip(b.iter()).map(|x, y| Some(x, y) => x * y).sum();
    println!("{}", r);
}

这失败了

error: expected one of `)`, `,`, `.`, `?`, or an operator, found `=>`
 --> src/main.rs:4:58
  |
4 |     let r = a.iter().zip(b.iter()).map(|x, y| Some(x, y) => x * y).sum();
  |                                                          ^^ expected one of `)`, `,`, `.`, `?`, or an operator here

我也试过这些，都失败了:

I've also tried these, all of which failed:

let r = a.iter().zip(b.iter()).map(|x, y| => x * y).sum();
let r = a.iter().zip(b.iter()).map(Some(x, y) => x * y).sum();

这样做的正确方法是什么?

What is the correct way of doing this?

(游乐场)

推荐答案

在 map() 中，您不必处理迭代器返回 Option 的事实代码>.这由 map() 处理.您需要提供一个函数，该函数采用两个借用值的元组.您的第二次尝试已接近尾声，但语法错误.这是正确的:

In map(), you don't have to deal with the fact that the iterator returns an Option. This is taken care of by map(). You need to supply a function taking the tuple of both borrowed values. You were close with your second try, but with the wrong syntax. This is the right one:

a.iter().zip(b.iter()).map(|(x, y)| x * y).sum()

您的最终程序需要在 r 上添加注释:

Your final program required an annotation on r:

fn main() {
    let a = vec![1, 2, 3, 4];
    let b = a.clone();

    let r: i32 = a.iter().zip(b.iter()).map(|(x, y)| x * y).sum();

    println!("{}", r);
}

(游乐场)

另见:

• 为什么 Rust 不能推断 Iterator::sum 的结果类型?
• 如何使用折叠对向量求和?

关于传递给 map 的闭包的更多信息:我写了 ...map(|(x, y)| x * y)，但是为了更复杂您需要使用 {} 分隔闭包主体的操作:

More info on the closure passed to map: I have written ...map(|(x, y)| x * y), but for more complicated operations you would need to delimit the closure body with {}:

.map(|(x, y)| {
    do_something();
    x * y
})

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