file extension as a parameter for ggsave to allow specific device matching

parameter to set if the filename extension cannot inform the proper
device to use (e.g. in a temp file)

Author: Sebastian Kopf

R/save.r

@@ -36,9 +36,9 @@
 #' ggsave("ratings.pdf", ratings, scale=2)
 #' }
 ggsave <- function(filename = default_name(plot), plot = last_plot(),
-  device = default_device(filename), path = NULL, scale = 1,
+  device = default_device(ext), path = NULL, scale = 1,
   width = par("din")[1], height = par("din")[2], units = c("in", "cm", "mm"),
-  dpi = 300, limitsize = TRUE, ...) {
+  dpi = 300, limitsize = TRUE, ext = default_ext(filename), ...) {
 
   if (!inherits(plot, "ggplot")) stop("plot should be a ggplot2 plot")
 
@@ -69,9 +69,12 @@ ggsave <- function(filename = default_name(plot), plot = last_plot(),
     paste(digest.ggplot(plot), ".pdf", sep="")
   }
 
-  default_device <- function(filename) {
+  default_ext <- function(filename) {
     pieces <- strsplit(filename, "\\.")[[1]]
     ext <- tolower(pieces[length(pieces)])
+  }
+  
+  default_device <- function(ext) {
     match.fun(ext)
   }