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I am writing a function that expects two arguments: X and Y. Argument X should be a raster which can be generated by packages such as raster, terra, or stars.

Argument Y should be a polygon from packages such as sp or sf. All these packages manage spatial data differently and represent this data using objects of different structure.

How can I ensure that the user supplied objects of the right classes to my function?

Currently, I managed only to test whether object X is of class RasterLayer (created by the package raster) and whether the object Y is of class SpatialPolygonsDataFrame (created by the package sp)

e.g.

  if(class(Y) != "SpatialPolygonsDataFrame"){
    stop("Y has to be a spatial object of type SpatialPolygonsDataFrame")
  }
  if(class(X) != "RasterLayer"){
    stop("X has to be an object of class RasterLayer")
  }
2
  • One efficient way to test for multiple classes is with any. Something along the lines of: if(!any(x %in% c("SpatRaster", "RasterLayer", "stars") ) you could then issue a stop as the condition. Commented Oct 18, 2021 at 14:55
  • Sorry, answered on my phone, x should be wrapped in class. Commented Oct 18, 2021 at 15:31

1 Answer 1

4

I'm doing pretty much the same

if (is(X, "RasterLayer") | is(X, "SpatRaster") | is(X, "stars"))
{
  # handle the different cases with specific code
  # personnally I convert to stars
}

if (is(X, "SpatialPolygonsDataFrame") | is(X, "sf"))
{
  # handle the different cases with specific code
  # personnally I convert to sf
}

In my case my code looks more like


if (inherit(X, "Spatial"))
  X <- sf::st_as_sf(X)

if (inherit(Y, "Raster"))
  Y <- stars::st_as_stars(Y)

if (inherit(Y, "SpatRaster"))
  Y <- stars::st_as_stars(Y) # that one does not exist do it yourself

if(!is(X, "sf"))
   stop("Y has to be a spatial object ")

if(!is(Y, "stars")
   stop("Y has to be a raster object")

geom = sf::st_geometry(X)

if (!is(geom, "sfc_POLYGON") & !is(geom, "sfc_MULTIPOLYGON"))
   stop("Y has to be a spatial polygon object ")

# keep going with sf/stars-based code

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