Leaflet: addPolygons can only add a single polygon

[hadley]

If you have a data frame - there needs to be some way to create multiple polygons from a single data frame (by specifying a variable that defines them)

[cawthm]

^^eg, given this df:
df <- data.frame(lat = c(36.1, 36, 36, 36.1, 36.1, 36, 36), lng = c(-94.17, -94.2, -94.14, -94.2, -94.14, -94.14, -94.2), shape = c("triangle", "triangle", "triangle", "square", "square", "square", "square"))

filtering on one polygon, this plots nicely:
df %>% filter(shape == "triangle") %>% leaflet() %>% addPolygons(lat = ~lat, lng = ~lng)

but this does not:
df %>% leaflet() %>% addPolygons(lat = ~lat, lng = ~lng)

Here is Hadley's shim:

l <- leaflet()
shapes <- unique(df$shape)
for (shape in shapes) {
d <- df[df$shape == shape, , drop = FALSE]
l <- l %>% addPolygons(lat = d$lat, lng = d$lng)
}
l

[jcheng5]

You could use this function to change the data frame to an sp::SpatialPolygons object, which works nicely with Leaflet:

library(dplyr)
library(sp)
library(leaflet)

dataframeToPolygons <- function(df, latCol, lngCol, idCol) {
  SpatialPolygons(lapply(unique(df[[idCol]]), function(id) {
    Polygons(list(Polygon(as.matrix(
      df[df[[idCol]] == id, c(lngCol, latCol)]
    ))), id)
  }))
}

df <- data.frame(lat = c(36.1, 36, 36, 36.1, 36.1, 36, 36), lng = c(-94.17, -94.2, -94.14, -94.2, -94.14, -94.14, -94.2), shape = c("triangle", "triangle", "triangle", "square", "square", "square", "square"))

df %>% dataframeToPolygons("lat", "lng", "shape") %>%
  leaflet() %>% addPolygons()

[hadley]

How about exposing id as an additional formula style parameter so people can continue to work with data frames without having to deal with the intricacies of sp?

[sethneel]

^did this ever get done? still seems like I need a for loop to iterate through and add multiple polygons. alternative is to use a spatial polygons data frame to create the leaflet object and then call addPolygons() but what if I just want to add the polygons to an existing map?

[jcheng5]

@sethneel You can do that, just pass a data argument to addPolygons: addPolygons(map, data = spobj, ...). Most layer functions in leaflet have a data parameter that overrides whatever you passed to leaflet() (if anything).