Added two functions, labeller and label_wrap_gen.

These two functions aid when labelling facets. labeller allows for
providing multiple named vectors and/or methods to change the labels for
each margin. label_wrap_gen allows labels to be word wrapped.

Author: stefanedwards

R/facet-labels.r

@@ -62,6 +62,67 @@ label_bquote <- function(expr = beta ^ .(x)) {
   }
 }
 
+#' Label facets with a word wrapped label.
+#' 
+#' Uses \code{\link[base]{strwrap}} for line wrapping.
+#' @param width integer, target column width for output.
+#' @export
+#' @seealso , \code{\link{labeller}}
+#' @examples
+#' set.seed(331)
+#' x=runif(60)
+#' y=rnorm(60)
+#' speed=sample(c('Prime group', 'Rib group', 'No group'), 60, replace=TRUE)
+#' group=sample(letters[1:3], 60, replace=TRUE)
+#' 
+#' df = data.frame(x=x, y=y, speed=as.factor(speed), group=as.factor(group))
+#' group.names <- c('a'='First','b'='Second','c'="Don\'t")
+#' 
+#' ggplot(df, aes(x, y)) + geom_point() + facet_grid(speed ~ group, labeller=label_wrap_gen(3))
+#' ggplot(df, aes(x, y)) + geom_point() + facet_grid(speed ~ group, labeller=labeller(speed=label_wrap_gen(3), group=group.names))
+label_wrap_gen <- function(width = 25) {
+  function(variable, value) {
+    lapply(strwrap(as.character(value), width=width, simplify=FALSE), 
+           paste, collapse="\n")
+  }
+}
+
+#' Generic labeller function for facets
+#' 
+#' One-step function for providing methods or named character vectors
+#' as labels in facets.
+#'
+#' @param keep.as.numbers logical, default TRUE. When FALSE, converts numeric values supplied as margins to the facet to characters.
+#' @family facet labeller
+#' @return Function to supply to \code{\link{facet_grid}} for the argument \code{labeller}.
+#' @export 
+#' @examples
+#' numbers <- c(`4`='four', `6`='six', `8`='eight')
+#' vs <- c(`0`='No vs', `1`='vs')
+#' p <- ggplot(mtcars, aes(mpg, wt)) + geom_point()
+#' p + facet_grid(vs~cyl, labeller=labeller(cyl=numbers, vs=vs))
+labeller <- function(keep.as.numeric=FALSE, ...) {
+  args <- list(...)
+  lbl <- function(variable, values) {
+    res <- args[[variable]]
+    if (is.numeric(values) & !keep.as.numeric) values <- as.character(values)
+    #print(str(variable))
+    #print(str(values))
+    
+    if (is.null(res)) {
+      if (is.factor(values)) return(levels(values[drop=TRUE]))
+      return(values)
+    }
+    if (is.function(res)) return(res(variable, values))
+    if (is.logical(values)) values <- as.integer(values)+1
+    if (is.factor(values)) values <- levels(values)[values]
+    return(res[values])
+  }
+  return(lbl)
+}
+
+
+
 # Grob for strip labels
 ggstrip <- function(text, horizontal=TRUE, theme) {
   text_theme <- if (horizontal) "strip.text.x" else "strip.text.y"