New themes panel.margin.x and panel.margin.y

Fixes #839

Conflicts:
	NEWS
	R/facet-grid-.r

Resolved trivially.

Author: Kirill Müller

NEWS

@@ -7,6 +7,9 @@ ggplot2 0.9.3.1.99
 * `ggpcp()`, `ggfluctuation()`, `ggmissing()`, `ggstructure()`, and
   `ggorder()` are now defunct and have been removed.
 
+* theme: new theme settings panel.margin.x and panel.margin.y (units) allow
+  specifying horizontal and vertical gap between panels in facetted plots (for
+  both grid and wrap).  (Kirill Müller. Fixes #839)
 
 ggplot2 0.9.3.1
 ----------------------------------------------------------------

R/facet-grid-.r

@@ -299,9 +299,9 @@ build_strip <- function(panel, label_df, labeller, theme, side = "right") {
   strips <- gtable_matrix(name, grobs, heights = heights, widths = widths)
 
   if (horizontal) {
-    gtable_add_col_space(strips, theme$panel.margin)
+    gtable_add_col_space(strips, theme$panel.margin.x %||% theme$panel.margin)
   } else {
-    gtable_add_row_space(strips, theme$panel.margin)
+    gtable_add_row_space(strips, theme$panel.margin.y %||% theme$panel.margin)
   }
 }
 
@@ -314,14 +314,14 @@ facet_axes.grid <- function(facet, panel, coord, theme) {
   grobs <- lapply(panel$ranges[cols], coord_render_axis_h,
     coord = coord, theme = theme)
   axes$b <- gtable_add_col_space(gtable_row("axis-b", grobs),
-    theme$panel.margin)
+    theme$panel.margin.x %||% theme$panel.margin)
 
   # Vertical axes
   rows <- which(panel$layout$COL == 1)
   grobs <- lapply(panel$ranges[rows], coord_render_axis_v,
     coord = coord, theme = theme)
   axes$l <- gtable_add_row_space(gtable_col("axis-l", grobs),
-    theme$panel.margin)
+    theme$panel.margin.y %||% theme$panel.margin)
 
   axes
 }
@@ -382,8 +382,8 @@ facet_panels.grid <- function(facet, panel, coord, theme, geom_grobs) {
 
   panels <- gtable_matrix("panel", panel_matrix,
     panel_widths, panel_heights, respect = respect)
-  panels <- gtable_add_col_space(panels, theme$panel.margin)
-  panels <- gtable_add_row_space(panels, theme$panel.margin)
+  panels <- gtable_add_col_space(panels, theme$panel.margin.x %||% theme$panel.margin)
+  panels <- gtable_add_row_space(panels, theme$panel.margin.y %||% theme$panel.margin)
 
   panels
 }

R/facet-wrap.r

@@ -164,13 +164,13 @@ facet_render.wrap <- function(facet, panel, coord, theme, geom_grobs) {
   # If not listed, assume is unit(1, "null")
   widths <- list(
     axis_l = width_cm(grobs$axis_l),
-    vspace = ifelse(layout$COL == ncol, 0, width_cm(theme$panel.margin))
+    vspace = ifelse(layout$COL == ncol, 0, width_cm(theme$panel.margin.x %||% theme$panel.margin))
   )
   heights <- list(
     panel = unit(aspect_ratio, "null"),
     strip_t = height_cm(grobs$strip_t),
     axis_b = height_cm(grobs$axis_b),
-    hspace = ifelse(layout$ROW == nrow, 0, height_cm(theme$panel.margin))
+    hspace = ifelse(layout$ROW == nrow, 0, height_cm(theme$panel.margin.y %||% theme$panel.margin))
   )
 
   col_widths <- compute_grob_widths(info, widths)

R/theme-defaults.r

@@ -46,6 +46,8 @@ theme_grey <- function(base_size = 12, base_family = "") {
     panel.grid.major =   element_line(colour = "white"),
     panel.grid.minor =   element_line(colour = "grey95", size = 0.25),
     panel.margin =       unit(0.25, "lines"),
+    panel.margin.x =     NULL,
+    panel.margin.y =     NULL,
 
     strip.background =   element_rect(fill = "grey80", colour = NA),
     strip.text.x =       element_text(),

R/theme-elements.r

@@ -306,6 +306,8 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
   panel.background    = el_def("element_rect", "rect"),
   panel.border        = el_def("element_rect", "rect"),
   panel.margin        = el_def("unit"),
+  panel.margin.x      = el_def("unit", "panel.margin"),
+  panel.margin.y      = el_def("unit", "panel.margin"),
   panel.grid.major.x  = el_def("element_line", "panel.grid.major"),
   panel.grid.major.y  = el_def("element_line", "panel.grid.major"),
   panel.grid.minor.x  = el_def("element_line", "panel.grid.minor"),

R/theme.r

@@ -135,6 +135,10 @@ print.theme <- function(x, ...) str(x)
 #'                    (\code{element_rect}; inherits from \code{rect}) \cr
 #'   panel.margin     \tab margin around facet panels
 #'                    (\code{unit}) \cr
+#'   panel.margin.x   \tab horizontal margin around facet panels
+#'                    (\code{unit}; inherits from \code{panel.margin}) \cr
+#'   panel.margin.y   \tab vertical margin around facet panels
+#'                    (\code{unit}; inherits from \code{panel.margin}) \cr
 #'   panel.grid       \tab grid lines
 #'                    (\code{element_line}; inherits from \code{line}) \cr
 #'   panel.grid.major \tab major grid lines
@@ -271,7 +275,7 @@ print.theme <- function(x, ...) str(x)
 #' k + theme(strip.text.x = element_text(colour = "red", angle = 45, size = 10,
 #'                                       hjust = 0.5, vjust = 0.5))
 #' k + theme(panel.margin = unit(5, "lines"))
-#' k + theme(panel.margin = unit(0, "lines"))
+#' k + theme(panel.margin.y = unit(0, "lines"))
 #'
 #'
 #' # Modify a theme and save it