Support grid = "x/y/X/Y"

DESCRIPTION

@@ -54,7 +54,7 @@ Suggests:
   knitr
 Config/Needs/website: altdoc (>= 0.7.2), future.apply
 Encoding: UTF-8
-RoxygenNote: 7.3.3
 URL: https://grantmcdermott.com/tinyplot/
 BugReports: https://github.com/grantmcdermott/tinyplot/issues
 Roxygen: list(markdown = TRUE)
+Config/roxygen2/version: 8.0.0

NEWS.md

@@ -32,9 +32,22 @@ where the formatting is also better._
 
 ### New features
 
+- The `grid` argument (and `tpar("grid")`) now accepts character strings to
+  control axis-specific grids at different resolutions. Uppercase letters
+  (`"X"`, `"Y"`, `"XY"`) draw grid lines at the standard tick positions, while
+  lowercase letters (`"x"`, `"y"`, `"xy"`) draw a finer grid with additional
+  lines at the midpoints between ticks. Thanks to @zeileis for the suggestion.
+  (#578 @grantmcdermott)
 - New `"dynamic"` theme that now serves as the foundation for all other dynamic
   (tiny)themes. (#549 @grantmcdermott) 
 
+### Bug fixes
+
+- Fixed `grid = grid()` not drawing grid lines on all facets. That said, logical
+  or character inputs (e.g., `grid = TRUE`, `grid = "xy"`) remain the more
+  idiomatic way to generate a background grid in `tinyplot`.
+  (#193 @grantmcdermott)
+
 ## v0.6.1
 
 ### Aesthetic changes

R/assertions.R

@@ -90,6 +90,15 @@ assert_length = function(x, len = 1, null.ok = FALSE, name = as.character(substi
   }
 }
 
+assert_grid = function(x, null.ok = FALSE, name = as.character(substitute(x))) {
+  if (is.null(x) && isTRUE(null.ok)) return(invisible(TRUE))
+  if (is.logical(x) && length(x) == 1) return(invisible(TRUE))
+  valid_strings = c("x", "y", "X", "Y", "xy", "xY", "Xy", "XY")
+  if (is.character(x) && length(x) == 1 && x %in% valid_strings) return(invisible(TRUE))
+  msg = sprintf("`%s` must be a logical flag or a character string combining x/X and/or y/Y (e.g., \"xy\", \"XY\", \"xY\")", name)
+  stop(msg, call. = FALSE)
+}
+
 assert_logical = function(x, null.ok = FALSE, name = as.character(substitute(x))) {
   if (is.null(x) && isTRUE(null.ok)) {
     return(invisible(TRUE))

R/facet.R

@@ -514,34 +514,54 @@ draw_facet_window = function(
 
     # panel grid lines
     if (is.null(grid)) grid = get_tpar("grid", tpar_list = tpars)
-    if (!is.null(grid)) {
-      if (is.logical(grid)) {
-        ## If grid is TRUE create a default grid. Rather than just calling the default grid()
-        ## abline(... = pretty(extendrange(...)), ...) is used. Reason: pretty() is generic
-        ## and works better for axes based on date/time classes. Exception: For axes in logs,
-        ## resort to using grid() which is likely better handled there.
-        if (isTRUE(grid)) {
-          gnx = gny = NULL
+    if (!is.null(grid) && !isFALSE(grid)) {
+      gcol = get_tpar("grid.col", tpar_list = tpars)
+      glty = get_tpar("grid.lty", tpar_list = tpars)
+      glwd = get_tpar("grid.lwd", tpar_list = tpars)
+
+      if (isTRUE(grid)) {
+        draw_x = draw_y = TRUE
+        fine_x = fine_y = FALSE
+      } else if (is.character(grid)) {
+        draw_x = grepl("x", grid, fixed = TRUE) || grepl("X", grid, fixed = TRUE)
+        draw_y = grepl("y", grid, fixed = TRUE) || grepl("Y", grid, fixed = TRUE)
+        fine_x = grepl("x", grid, fixed = TRUE)
+        fine_y = grepl("y", grid, fixed = TRUE)
+      } else {
+        eval(grid) # issue #193
+        draw_x = draw_y = FALSE
+      }
+
+      if (draw_x || draw_y) {
+
+        if (draw_x) {
           if (!is.null(xaxb)) {
-            abline(v = xaxb, col = get_tpar("grid.col", tpar_list = tpars), lty = get_tpar("grid.lty", tpar_list = tpars), lwd = get_tpar("grid.lwd", tpar_list = tpars))
-            gnx = NA
-          } else if (!any(c(par("xlog"), type == "boxplot"))) {
+            xg = xaxb
+          } else {
             xg = if (!inherits(x, c("POSIXt", "Date"))) axTicks(side = 1) else axTicksDateTime(side = 1, x = x)
-            abline(v = xg, col = get_tpar("grid.col", tpar_list = tpars), lty = get_tpar("grid.lty", tpar_list = tpars), lwd = get_tpar("grid.lwd", tpar_list = tpars))
-            gnx = NA
           }
+          if (fine_x && !par("xlog") && length(xg) >= 2L) {
+            xg = as.numeric(xg)
+            half = (xg[2L] - xg[1L]) / 2
+            xg = seq(xg[1L] - half, xg[length(xg)] + half, by = half)
+          }
+          abline(v = xg, col = gcol, lty = glty, lwd = glwd)
+        }
+
+        if (draw_y) {
           if (!is.null(yaxb)) {
-            abline(h = yaxb, col = get_tpar("grid.col", tpar_list = tpars), lty = get_tpar("grid.lty", tpar_list = tpars), lwd = get_tpar("grid.lwd", tpar_list = tpars))
-            gny = NA
-          } else if (!any(c(par("ylog"), type == "boxplot"))) {
+            yg = yaxb
+          } else {
             yg = if (!inherits(y, c("POSIXt", "Date"))) axTicks(side = 2) else axTicksDateTime(side = 2, x = x)
-            abline(h = yg, col = get_tpar("grid.col", tpar_list = tpars), lty = get_tpar("grid.lty", tpar_list = tpars), lwd = get_tpar("grid.lwd", tpar_list = tpars))
-            gny = NA
           }
-          grid(nx = gnx, ny = gny, col = get_tpar("grid.col", tpar_list = tpars), lty = get_tpar("grid.lty", tpar_list = tpars), lwd = get_tpar("grid.lwd", tpar_list = tpars))
+          if (fine_y && !par("ylog") && length(yg) >= 2L) {
+            yg = as.numeric(yg)
+            half = (yg[2L] - yg[1L]) / 2
+            yg = seq(yg[1L] - half, yg[length(yg)] + half, by = half)
+          }
+          abline(h = yg, col = gcol, lty = glty, lwd = glwd)
         }
-      } else {
-        grid
+
       }
     }
 

R/tinyplot.R

@@ -197,8 +197,15 @@
 #'   the plot. Can also use `frame` as an acceptable argument alias.
 #'   The default is to draw a frame if both axis types (set via `axes`, `xaxt`,
 #'   or `yaxt`) include axis lines.
-#' @param grid argument for plotting a background panel grid, one of either:
-#'    - a logical (i.e., `TRUE` to draw the grid), or
+#' @param grid argument for plotting a background panel grid, one of:
+#'    - a logical (i.e., `TRUE` to draw the grid on both axes).
+#'    - a character string controlling which axes get grid lines and at what
+#'      resolution. Uppercase letters (`"X"`, `"Y"`, `"XY"`) draw grid lines at
+#'      the standard axis tick positions (with the latter equivalent to `TRUE`),
+#'      while lowercase letters (`"x"`, `"y"`, `"xy"`) draw a finer grid with
+#'      additional lines at the midpoints between ticks. (Note: the finer grid
+#'      has no effect on log-scale axes, since tick positions already include
+#'      intermediate values.)
 #'    - a panel grid plotting function like `grid()`.
 #'   Note that this argument replaces the `panel.first` and `panel.last`
 #'   arguments from base `plot()` and tries to make the process more seamless
@@ -653,6 +660,12 @@ tinyplot.default = function(
   par_first = get_saved_par("first")
   if (is.null(par_first)) set_saved_par("first", par())
 
+  # Validate grid only for simple values; skip for unevaluated calls like grid()
+  # which are passed as language objects from tinyplot.formula via substitute(). (#193)
+  if (!is.null(grid) && !is.call(grid)) {
+    assert_grid(grid, null.ok = TRUE, name = "grid")
+  }
+
   # save for tinyplot_add()
   assert_logical(add)
   if (!add) {
@@ -1580,7 +1593,7 @@ tinyplot.formula = function(
     axes = axes,
     frame.plot = frame.plot,
     asp = asp,
-    grid = grid,
+    grid = substitute(grid), # issue #193
     legend_args = legend_args,
     pch = pch,
     col = col,

R/tpar.R

@@ -65,7 +65,7 @@
 #' * `grid.col`: Character or (integer) numeric that specifies the color of the panel grid lines. Defaults to `"lightgray"`.
 #' * `grid.lty`: Character or (integer) numeric that specifies the line type of the panel grid lines. Defaults to `"dotted"`.
 #' * `grid.lwd`: Non-negative numeric giving the line width of the panel grid lines. Defaults to `1`.
-#' * `grid`: Logical indicating whether a background panel grid should be added to plots automatically. Defaults to `NULL`, which is equivalent to `FALSE`.
+#' * `grid`: Logical or character indicating whether a background panel grid should be added to plots automatically. Defaults to `NULL`, which is equivalent to `FALSE`. In addition to logical values, a character string can be used to control axis-specific grids: uppercase letters (`"X"`, `"Y"`, `"XY"`) draw grid lines at the standard axis tick positions (equivalent to `TRUE`), while lowercase letters (`"x"`, `"y"`, `"xy"`) draw a finer grid with additional lines at the midpoints between ticks.
 #' * `lmar`: A numeric vector of form `c(inner, outer)` that gives the margin padding, in terms of lines, around the automatic `tinyplot` legend. Defaults to `c(1.0, 0.1)`. The inner margin is the gap between the legend and the plot region, and the outer margin is the gap between the legend and the edge of the graphics device.
 #' * `palette.qualitative`: Palette for qualitative colors. See the `palette` argument in `?tinyplot`.
 #' * `palette.sequential`: Palette for sequential colors. See the `palette` argument in `?tinyplot`.
@@ -276,7 +276,7 @@ assert_tpar = function(.tpar) {
   assert_numeric(.tpar[["lmar"]], len = 2, null.ok = TRUE, name = "lmar")
   assert_numeric(.tpar[["ribbon.alpha"]], len = 1, lower = 0, upper = 1, null.ok = TRUE, name = "ribbon.alpha")
   assert_numeric(.tpar[["grid.lwd"]], len = 1, lower = 0, null.ok = TRUE, name = "grid.lwd")
-  assert_flag(.tpar[["grid"]], null.ok = TRUE, name = "grid")
+  assert_grid(.tpar[["grid"]], null.ok = TRUE, name = "grid")
   assert_numeric(.tpar[["file.res"]], len = 1, lower = 0, null.ok = TRUE, name = "file.res")
   assert_numeric(.tpar[["file.height"]], len = 1, lower = 0, null.ok = TRUE, name = "file.height")
   assert_numeric(.tpar[["file.width"]], len = 1, lower = 0, null.ok = TRUE, name = "file.width")