internal function shares_border return NULL

[ggrittz]

`

a = plantR:::shares_border(country = 'united kingdom', country2 = 'ireland')
a
NULL
`

The polis object is an integer of value 5L and poli_u of value 7L, which does not fit any of the conditions required to return the logical FALSE/TRUE.

polis <- nrow(v) + nrow(z)
  poli_u <- nrow(y)
  if (polis == poli_u) 
    return(FALSE)
  if (poli_u < polis) 
    return(TRUE)
}

The issue arises due to geographical units with multiple polygons in the plantR::world object, e.g., United Kingdom, Somalia, Canada, Argentina...and so on.

> v
Simple feature collection with 2 features and 2 fields
Geometry type: MULTIPOLYGON
Dimension:     XY
Bounding box:  xmin: 40.98105 ymin: -1.68325 xmax: 51.13387 ymax: 12.02464
Geodetic CRS:  WGS 84
    iso_a2    name                       geometry
12      SO somalia MULTIPOLYGON (((41.58513 -1...
171   <NA> somalia MULTIPOLYGON (((48.9482 11....

Due to that, I simplified the function to use sf::st_intersects instead of counting the number of polygons:

my_shares_border <- function(country1 = "ireland", country2 = "united kingdom") {
  world <- world
  w <- world

  if (!country1 %in% w$name) 
    country1 <- plantR::prepLoc(plantR::prepCountry(country1))
  if (!country2 %in% w$name) 
    country2 <- plantR::prepLoc(plantR::prepCountry(country2))
  if (!country1 %in% w$name | !country2 %in% w$name) 
    stop(paste0("Country name(s) '", c(country1, 
                                       country2)[!c(country1,
                                                    country2) %in% w$name], "' not found"))
  v <- w[w$name %in% c(country1), ]
  z <- w[w$name %in% c(country2), ]
  intersects <- sf::st_intersects(v, z, sparse = FALSE)[1, 1]
  return(intersects)
}

a = my_shares_border(country1 = 'united kingdom', country2 = 'ireland')
a

If wanted, it's possible to add a buffer to each country before using sf::st_intersects