remove_geom: a function to remove layers from a ggplot2 object

DESCRIPTION

@@ -205,3 +205,4 @@ Collate:
     'translate-qplot-lattice.r'
     'annotation-logticks.r'
     'utilities-help.r'
+    'remove-geom.R'

NAMESPACE

@@ -289,6 +289,7 @@ export(position_stack)
 export(qplot)
 export(quickplot)
 export(rel)
+export(remove_geom)
 export(resolution)
 export(scale_alpha)
 export(scale_alpha_continuous)

NEWS

@@ -1,6 +1,9 @@
 ggplot2 0.9.3.99
 ----------------------------------------------------------------
 
+* New function `remove_geom` to remove specific layers from a ggplot2
+  object.
+
 BUG FIXES
 
 * The theme element `legend.box.just` now can be set. It was not properly

R/remove-geom.R

@@ -0,0 +1,28 @@
+#' Remove a Geom From a ggplot2 Object
+#'
+#' remove_geom allows you to remove layers of from a ggplot2 object
+#' by specifying the name of a geom to remove. This can be useful 
+#' when dynamically building ggplot2 objects and want to remove
+#' cluttered layers that have already been added to the object in
+#' previous function calls.
+#'
+#' @param plot_object the ggplot2 object to work on
+#' @param geom name of geom to remove
+#' @examples
+#' p <- ggplot(data.frame(a=1:10, b=1:10), aes(x=a, y=b)) + geom_point() + geom_line()
+#' p_minus_point <- remove_geom(p, "point")
+#' stopifnot(
+#'   setdiff(
+#'     sapply(p$layers, function(x) x$geom$objname), 
+#'     sapply(p_minus_point$layers, function(x) x$geom$objname)
+#'   ) == "point"
+#' )
+#' @export
+remove_geom <- function(plot_object, geom) {
+
+  layers <- lapply(plot_object$layers, function(x) if(x$geom$objname == geom) NULL else x)
+  layers <- layers[!sapply(layers, is.null)]
+
+  plot_object$layers <- layers
+  plot_object
+}

man/remove_geom.Rd

@@ -0,0 +1,29 @@
+\name{remove_geom}
+\alias{remove_geom}
+\title{Remove a Geom From a ggplot2 Object}
+\usage{
+  remove_geom(plot_object, geom)
+}
+\arguments{
+  \item{plot_object}{the ggplot2 object to work on}
+
+  \item{geom}{name of geom to remove}
+}
+\description{
+  remove_geom allows you to remove layers of from a ggplot2
+  object by specifying the name of a geom to remove. This
+  can be useful when dynamically building ggplot2 objects
+  and want to remove cluttered layers that have already
+  been added to the object in previous function calls.
+}
+\examples{
+p <- ggplot(data.frame(a=1:10, b=1:10), aes(x=a, y=b)) + geom_point() + geom_line()
+p_minus_point <- remove_geom(p, "point")
+stopifnot(
+  setdiff(
+    sapply(p$layers, function(x) x$geom$objname),
+    sapply(p_minus_point$layers, function(x) x$geom$objname)
+  ) == "point"
+)
+}
+