add a demo of routing sf to geojson layer

This approach should still be useful for strange corner-cases (i.e., rings, holes) where we can't quite completely replicate geom_sf(). Note, however, when using layers, you lose the ability to tie data semantices to each feature (and, thus, lose the ability to link multiple views)

Author: cpsievert

demo/sf-scattermapbox.R

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+library(albersusa)
+library(sf)
+library(dplyr)
+library(plotly)
+
+d <- counties_sf() %>%
+  st_transform('+proj=longlat +datum=WGS84') %>%
+  filter(!state %in% c("Alaska", "Hawaii"))
+
+# TODO: is there a way to do this without writing to disk?
+sf_to_geojson <- function(x) {
+  tmp <- tempfile(fileext = ".geojson")
+  st_write(x, tmp, driver = "GEOJSON")
+  geojsonio::geojson_read(tmp, "local")
+}
+
+plot_mapbox(lat = 45.5017, lon = -73.5673) %>%
+  layout(
+    height = 600,
+    autosize = TRUE,
+    hovermode = 'closest',
+    mapbox = list(
+      layers = list(
+        list(
+          sourcetype = 'geojson',
+          source = sf_to_geojson(d),
+          type = 'fill',
+          color = 'transparent'
+        )
+      ),
+      bearing = 0,
+      center = list(lat = 27.8, lon = -83),
+      pitch = 0,
+      zoom = 5.2,
+      style = 'light'
+    )
+  )