r - ggmap - how do I manipulate the underlying raster?

Question

library(ggmap)

basemap <- get_googlemap(zoom = 15, scale = 4,format="png8", maptype="terrain")
ggmap(basemap) # OK

switch_bg <- function(x) {
  xc <- col2rgb(x)
  g <- xc["green",]
  b <- xc["blue",]
  xc["green",] <- b
  xc["blue",] <- g
  rgb(xc[1,], xc[2,], xc[3,], maxColorValue=255)
}
basemap[] <- switch_bg(basemap)
class(basemap) <- c("ggmap", "raster")

ggmap(basemap) # Does not plot

I want to manipulate the color of a ggmap. Since the raster is a matrix of colors, I thought I can just update the matrix. However, assigning to the matrix removes the class and somehow breaks the object.

Why?

Answer 1

等待大神答复