Issue plotting generated polygon grid to leaflet

Question

I am trying to create a polygon grid to plot in leaflet, but am running into an error that I cannot seem to figure out:

library(leaflet)
library(raster)
library(sf)
library(rgdal)

r <- raster(ext = extent(-10,0, -5, 5), res=c(1,1))
p <- rasterToPolygons(r) 
p <- st_as_sf(p)

leaflet() %>%
  addTiles() %>%
  addPolygons(p)

I get the error:

Error in derivePolygons(data, lng, lat, missing(lng), missing(lat), "addPolygons") : 
  addPolygons must be called with both lng and lat, or with neither.

I know that this is being thrown by the addPolygons() call, but I cannot seem to figure out what is doing it or how to fix it.

Answer 1

You are passing the polygon object in your leaflet::addPolygons() call by position; it will be passed to the second argument (since we are in a pipe).

The second position argument is lng for longitude. As a result your leaflet object will have longitude specified, and latitude missing.

What you need to do is pass the object by name = as data argument. This can happen both in your addPolygons() call or in the base leafet() call.

library(leaflet)
library(raster)
library(sf)
library(rgdal)

r <- raster(ext = extent(-10, 0, -5, 5), res=c(1,1))
p <- rasterToPolygons(r) 
p <- st_as_sf(p)

leaflet() %>%
  addTiles() %>%
  addPolygons(data = p) # see what I have done? :)