How can I process a string of numbers in Rust?

Question

I have an input:

let b = String::from("1 2 4 5 6");

And my task is to return the exponential function of each value as a string as output:

let output = "2.718281828459045 7.38905609893065 54.598150033144236 148.4131591025766 403.4287934927351";

I have no idea how to solve this task. How to parse each value and use exp function and send string of the result?

score 5 · Answer 1 · answered Feb 16 '21 at 13:12

Here's the ingredients:

Split the string: How do I split a string in Rust?
Convert each part to f64 (or f32): https://programming-idioms.org/idiom/146/convert-string-to-floating-point-number/1974/rust
Exponentiate each number: https://doc.rust-lang.org/std/primitive.f64.html#method.exp
Convert results to string: How can I convert a float to string?
Concatenate into single string: https://stackoverflow.com/a/41688369

pretzelhammer · Answer 2 · 2021-02-17T00:50:47.910

2

I'm not going to repeat what phimuemue has already explained so here's an implementation:

fn example(s: &str) -> String {
    s.trim()
        .split_whitespace()
        .map(|n| {
            let mut n = n.parse::<f64>().unwrap();
            n = n.exp();
            n.to_string()
        })
        .collect::<Vec<String>>()
        .join(" ")
}

fn main() {
    let input = String::from("1 2 4 5 6");
    let output = example(&input);
    dbg!(output); // "2.718281828459045 7.3890560989306495 54.59815003314423 148.41315910257657 403.428793492735"
}

playground

edited Feb 17 '21 at 00:50

answered Feb 16 '21 at 13:15

pretzelhammer

12,263
15
41
88

Or using [`Itertools::join`](https://docs.rs/itertools/0.10.0/itertools/trait.Itertools.html#method.join): https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=ce539a2fbc815184fe85c1488c84f60e – Jmb Feb 16 '21 at 14:37

How can I process a string of numbers in Rust?

2 Answers2