Partial margins

NAMESPACE

@@ -96,6 +96,7 @@ S3method(makeContext,dotstackGrob)
 S3method(merge_element,default)
 S3method(merge_element,element)
 S3method(merge_element,element_blank)
+S3method(merge_element,margin)
 S3method(pattern_alpha,GridPattern)
 S3method(pattern_alpha,GridTilingPattern)
 S3method(pattern_alpha,default)
@@ -484,6 +485,7 @@ export(layer_sf)
 export(lims)
 export(map_data)
 export(margin)
+export(margin_part)
 export(max_height)
 export(max_width)
 export(mean_cl_boot)

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Theme margins can have NA-units to inherit from parent elements. The new
+  function `margin_part()` has NA-units as default (@teunbrand, #6155)
 * Built-in `theme_*()` functions now have `ink` and `paper` arguments to control
   foreground and background colours respectively (@teunbrand)
 * The `summary()` method for ggplots is now more terse about facets 

R/margins.R

@@ -8,6 +8,13 @@ margin <- function(t = 0, r = 0, b = 0, l = 0, unit = "pt") {
   class(u) <- c("margin", class(u))
   u
 }
+
+#' @rdname element
+#' @export
+margin_part <- function(t = NA, r = NA, b = NA, l = NA, unit = "pt") {
+  margin(t = t, r = r, b = b, l = l, unit = unit)
+}
+
 is.margin <- function(x) {
   inherits(x, "margin")
 }

R/theme-elements.R

@@ -11,7 +11,7 @@
 #'   - `element_geom()`: defaults for drawing layers.
 #'
 #' `rel()` is used to specify sizes relative to the parent,
-#' `margin()` is used to specify the margins of elements.
+#' `margin()` and `margin_part()` are used to specify the margins of elements.
 #'
 #' @param fill Fill colour.
 #' @param colour,color Line/border colour. Color is an alias for colour.

R/theme.R

@@ -831,6 +831,18 @@
   new
 }
 
+#' @rdname merge_element
+#' @export
+merge_element.margin <- function(new, old) {
+  if (is.null(old) || inherits(old, "element_blank")) {
+    return(new)
+  }
+  if (anyNA(new)) {
+    new[is.na(new)] <- old[is.na(new)]
+  }
+  new
+}
+
 #' Combine the properties of two elements
 #'
 #' @param e1 An element object
@@ -864,6 +876,15 @@
     return(e1)
   }
 
+  if (inherits(e1, "margin") && inherits(e2, "margin")) {
+    if (anyNA(e2)) {
+      e2[is.na(e2)] <- unit(0, "pt")
+    }
+    if (anyNA(e1)) {
+      e1[is.na(e1)] <- e2[is.na(e1)]
+    }
+  }
+
   # If neither of e1 or e2 are element_* objects, return e1
   if (!inherits(e1, "element") && !inherits(e2, "element")) {
     return(e1)
@@ -893,6 +914,10 @@
     e1$linewidth <- e2$linewidth * unclass(e1$linewidth)
   }
 
+  if (inherits(e1, "element_text")) {
+    e1$margin <- combine_elements(e1$margin, e2$margin)
+  }
+
   # If e2 is 'richer' than e1, fill e2 with e1 parameters
   if (is.subclass(e2, e1)) {
     new <- defaults(e1, e2)

tests/testthat/test-theme.R

@@ -616,6 +616,22 @@ test_that("complete_theme completes a theme", {
   reset_theme_settings()
 })
 
+test_that("margin_part() mechanics work as expected", {
+
+  t <- theme_gray() +
+    theme(plot.margin = margin_part(b = 11))
+
+  test <- calc_element("plot.margin", t)
+  expect_equal(as.numeric(test), c(5.5, 5.5, 11, 5.5))
+
+  t <- theme_gray() +
+    theme(margins = margin_part(b = 11))
+
+  test <- calc_element("plot.margin", t)
+  expect_equal(as.numeric(test), c(5.5, 5.5, 11, 5.5))
+
+})
+
 # Visual tests ------------------------------------------------------------
 
 test_that("aspect ratio is honored", {