Convert ggfortify to sf

convertToSF.R

library(dplyr)

convertToSF <- function(df, id = "id", group = "group") {
  # Extract the non-polygon data.
  data <- df %>%
    group_by_(id) %>%
    do(head(., 1)) %>%
    .[,setdiff(names(.), c("long", "lat", "order", "hole", "piece", "group"))]

  # Extract the shapes. I don't know if this does the right
  # thing with holes--are holes even supported by ggfortify?
  features <- state.map %>%
    group_by_(id, group) %>%
    do(shape = list(cbind(.$long, .$lat))) %>%
    ungroup() %>%
    group_by_(id) %>%
    do(shapes = sf::st_multipolygon(.$shape)) %>%
    .$shapes %>%
    sf::st_sfc()
  
  sf::st_sf(features, data)
}