add as.gtable() method (#421)

Author: teunbrand

DESCRIPTION

@@ -20,7 +20,7 @@ License: MIT + file LICENSE
 Encoding: UTF-8
 Imports: 
     ggplot2 (>= 3.0.0),
-    gtable,
+    gtable (>= 0.3.6),
     grid,
     stats,
     grDevices,

NAMESPACE

@@ -9,6 +9,7 @@ S3method("[[<-",patchwork)
 S3method("|",ggplot)
 S3method(add_patches,ggplot)
 S3method(add_patches,patchwork)
+S3method(as.gtable,patchwork)
 S3method(as.list,patchwork)
 S3method(as_patch,formula)
 S3method(as_patch,gList)
@@ -150,6 +151,7 @@ importFrom(grid,upViewport)
 importFrom(grid,valid.just)
 importFrom(grid,viewport)
 importFrom(grid,widthDetails)
+importFrom(gtable,as.gtable)
 importFrom(gtable,gtable)
 importFrom(gtable,gtable_add_cols)
 importFrom(gtable,gtable_add_grob)

R/plot_patchwork.R

@@ -290,6 +290,11 @@ patchworkGrob <- function(x) {
   class(gtable) <- setdiff(class(gtable), 'gtable_patchwork')
   gtable
 }
+
+#' @importFrom gtable as.gtable
+#' @export
+as.gtable.patchwork <- function(x, ...) patchworkGrob(x)
+
 plot_table <- function(x, guides) {
   UseMethod('plot_table')
 }