36  Vectorize decode()

Objective

Create a vectorized gh_decode() function utilizing much of what we have learned today.

In addition to collecting an interator into a wrapper type—e.g. Doubles or Strings we can create a vector of scalar types—Vec<Rfloat> and create Doubles from that using the associated function Doubles::from_values(my_vec)

Using Doubles::from_values() is a flexible way to use Rust’s vectors and quickly translate them to R ones.

Example

// instantiate empty vector
let mut my_vec = Vec::new();

// iterate through something and push into the vector
for xi in x {
    my_vec.push(Rfloat::from(xi));
}

// Create a double vector from the vector
let res = Doubles::from_values(my_vec);

Exercise

Your objective for this exercise is to vectorize gh_decode() and return a data.frame. To do this:

• Create 4 empty vectors to store x, y, x_error, and y_error
• Iterate through each geohash and attempt to decode it
• For each successful decoding insert the x, y, and error values into their corresponding vectors
• When an error is encountered, insert NA values into the vectors
• Create double vectors for each variable using Doubles::from_values()
• Create a data.frame using data_frame!()

View solution

fn gh_decode(geohash: Strings) -> Robj {
    let mut x_res = Vec::new();
    let mut y_res = Vec::new();
    let mut x_error = Vec::new();
    let mut y_error = Vec::new();

    for gh in geohash.into_iter() {
        let resi = decode(gh);
        match resi {
            Ok((Coord { x, y }, xe, ye)) => {
                x_res.push(Rfloat::from(x));
                y_res.push(Rfloat::from(y));
                x_error.push(Rfloat::from(xe));
                y_error.push(Rfloat::from(ye));
            }
            Err(_) => {
                x_res.push(Rfloat::na());
                y_res.push(Rfloat::na());
                x_error.push(Rfloat::na());
                y_error.push(Rfloat::na());
            }
        }
    }

    data_frame!(
        x = Doubles::from_values(x_res),
        y = Doubles::from_values(y_res),
        x_error = Doubles::from_values(x_error),
        y_error = Doubles::from_values(y_error)
    )
}