Rust extendr/rextendr code to take R's data.frame as input, modify it (add columns), and return a modified data.frame

lib.rs

use extendr_api::prelude::*;
use rand::{distributions::Alphanumeric, Rng};
use std::collections::HashMap;

// Define the function to be used in R
#[extendr]
fn add_columns(df: Dataframe<Robj>) -> List {
    // Get the number of rows in the data frame
    let n_rows = df.get_attrib("row.names").unwrap().len();

    // Create a vector with row numbers.
    let row_numbers: Vec<i32> = (1..=n_rows as i32).collect();

    // Create a vector of random strings of random length (up to 10 characters)
    let random_strings: Vec<String> = (0..n_rows)
        .map( |_| rand::thread_rng()
        .sample_iter(&Alphanumeric)
        .take(rand::thread_rng().gen_range(1..=10) as usize)
        .map(char::from).collect() )
        .collect();

    // Convert the original dataframe to a list and add new columns
    let mut map: HashMap<&str, Robj> = HashMap::new();
    for (name, column) in df.as_list().unwrap().iter() {
        map.insert(name, column.clone()); // Column order random / not guaranteed!!!
    }
    map.insert("row_number", r!(row_numbers)); // Column order random / not guaranteed!!!
    map.insert("random_string", r!(random_strings)); // Column order random / not guaranteed!!!

    // Create a new List from the HashMap
    let mut df_list = List::from_hashmap(map).unwrap();
    
    // Convert StrIter to Vec<String> to use with set_attrib
    let names_vec: Vec<String> = df_list.names().unwrap().map(|s| s.to_string()).collect();
    // Convert (effectively) the list to a dataframe
    let _ = df_list.set_attrib("class", ["data.frame"]);
    let _ = df_list.set_attrib("names", names_vec);
    let _ = df_list.set_attrib("row.names", df.get_attrib("row.names").unwrap());
    
    // Return the modified data frame.
    df_list // Column order random / not guaranteed!!!
}

// Macro to generate exports
extendr_module! {
    mod mymodule;
    fn add_columns;
}

// Note: Make sure to add `rand` as a dependency in your `Cargo.toml`, like so:
// 
// [dependencies]
// extendr-api = "0.7"
// rand = "0.8"

> add_columns(data.frame(Aaa=101:110))

   random_string Aaa row_number
1       HjwLcacb 101          1
2          arKMI 102          2
3             sS 103          3
4              C 104          4
5     0lIM4zoHGC 105          5
6        HG7aSp2 106          6
7     7xLHYkLu0h 107          7
8     3l04gC5IIa 108          8
9      rqXFFIES2 109          9
10    my72MUjgWw 110         10