use ::std::{
  *,
  iter::FromIterator,
};

struct Key(usize, Box<str>);

const KEY: &str = "Key";

impl str::FromStr for Key {
  type Err = ();

  fn from_str(s: &str) -> Result<Self, Self::Err>
  {
    let mut s = s.split("=");
    match (s.next(), s.next()) {
      (Some(key), Some(value)) if key.starts_with(KEY) => {
        Ok(Key(key[KEY.len() ..].parse().map_err(mem::drop)?, value.into()))
      },
      _ => Err(()),
    }
  }
}


fn main() {
    let input = "Key0=value,Key3=vvalue,Key2=vealue,Key10=vralue,Key4=vtalue,Key1=vyalue,Key17=vualue".to_owned();

    let mut kvs = Vec::
      from_iter(
        (0 .. 100).map(|_| None)
      )
    ;
    input
      .split(",")
      .filter_map(|s| s.trim().parse().ok())
      .for_each(|Key(id, value)| kvs[id] = Some(value))
    ;

    println!("{:?}", itertools::join(kvs.iter().enumerate().filter_map(|(keyid,opt)|match opt{
        None => None,
        Some(value) => Some(format!("Key{}={}",keyid,value))
    }),","));
}