33  Geohash Neighbor

Objective

Create an R function that finds a directional neighbor for a geohash.

We now know how to take a string in R and convert it into an enum and what a &str is.

We’re going to begin building up a gh_neighbor() function which takes two arguments:

pub fn neighbor(
    hash_str: &str,
    direction: Direction,
) -> Result<String, GeohashError>

and returns a geohash as a string. We’re going to create an R wrapper to this function.

Exercise

• Create a new function gh_encode() which has two arguments: geohash: String, and direction: String and returns a String
• Import neighbor() from geohash
• Use as_direction() to process the direction arguments
• Use neighbor() to return the resultant geohash (you can unwrap for now)
  • Note: borrow geohash as neighbor() expects a &str—i.e. neighbor(&geohash, ...)

View solution

#[extendr]
fn gh_neighbor(geohash: String, direction: String) -> String {
    let dir = as_direction(direction);
    neighbor(&geohash, dir).unwrap()
}