find the standard deviation of all keys in a map in rust

To calculate the standard deviation of all keys in a map in Rust, you can follow these steps:

1. Import the stats module from the statrs crate, which provides statistical functions.
2. Extract all keys from the map as a vector.
3. Calculate the mean of the vector using the mean function from the stats module.
4. Calculate the variance of the vector using the variance function from the stats module, passing the mean calculated in step 3 as the second parameter.
5. Calculate the standard deviation of the vector using the stddev function from the stats module, passing the variance calculated in step 4 as the parameter.

Here's the code that implements the above steps:

main.rs
use statrs::statistics::{Statistics, Data};

fn main() {
    let mut map = std::collections::HashMap::new();
    map.insert(1, "One");
    map.insert(2, "Two");
    map.insert(3, "Three");
    map.insert(4, "Four");
    map.insert(5, "Five");

    let keys: Vec<i32> = map.keys().copied().collect();

    let mean = Data::new(&keys).mean().unwrap();
    let variance = Data::new(&keys).variance(Some(mean)).unwrap();
    let std_dev = Data::new(&keys).std_dev(Some(mean)).unwrap();

    println!("Standard deviation of map keys: {}", std_dev)
}
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In this example, a HashMap is created with integer keys and string values. The keys are then extracted as a vector, which is used to calculate the standard deviation of the keys using the previously mentioned steps. The result is then printed.