facetAnchor: empty (#1287)

Author: Fil

README.md

@@ -593,6 +593,7 @@ The <a name="facetanchor">*mark*.**facetAnchor**</a> option controls the placeme
 * null - display the mark on each non-empty facet (default for all marks, with the exception of axis marks)
 * *top*, *right*, *bottom*, or *left* - display the mark on facets on the specified side
 * *top-empty*, *right-empty*, *bottom-empty*, or *left-empty* - display the mark on facets that have an empty space on the specified side (the empty space being either the margin, or an empty facet); this is the default for axis marks
+* *empty* - display the mark on empty facets only
 
 ## Legends
 

src/facet.js

@@ -91,7 +91,8 @@ const facetAnchors = new Map([
   ["top-empty", facetAnchorTopEmpty],
   ["right-empty", facetAnchorRightEmpty],
   ["bottom-empty", facetAnchorBottomEmpty],
-  ["left-empty", facetAnchorLeftEmpty]
+  ["left-empty", facetAnchorLeftEmpty],
+  ["empty", facetAnchorEmpty]
 ]);
 
 export function maybeFacetAnchor(facetAnchor) {
@@ -153,6 +154,10 @@ function facetAnchorRightEmpty(facets, {x: X}, {x, y, empty}) {
   }
 }
 
+function facetAnchorEmpty(facets, channels, {empty}) {
+  return empty;
+}
+
 function and(a, b) {
   return function () {
     return a.apply(null, arguments) && b.apply(null, arguments);

test/output/futureSplom.svg

@@ -1,4 +1,5 @@
 import * as Plot from "@observablehq/plot";
+import * as d3 from "d3";
 
 export async function frameCorners() {
   return Plot.frame({rx: 16, ry: 10}).plot();
@@ -26,3 +27,27 @@ export async function frameSidesX() {
 export async function frameSidesY() {
   return Plot.plot({width: 350, height: 250, y: {domain: [0, 1]}, marks});
 }
+
+export async function futureSplom() {
+  const data = {columns: ["A", "B", "C"]};
+  return Plot.plot({
+    width: 400,
+    height: 400,
+    fx: {domain: data.columns, axis: null},
+    fy: {domain: data.columns, axis: null},
+    x: {type: "linear", domain: [-1.5, 1.5]},
+    y: {type: "linear", domain: [-1.5, 1.5]},
+    marks: [
+      Plot.gridX({ticks: 7}),
+      Plot.gridY({ticks: 7}),
+      Plot.axisX({facetAnchor: "bottom", ticks: 3}),
+      Plot.axisY({facetAnchor: "left", ticks: 3}),
+      Plot.text(
+        d3.cross(data.columns, data.columns).filter(([key1, key2]) => key2 !== key1),
+        {fx: "0", fy: "1", text: () => "*", frameAnchor: "middle"}
+      ),
+      Plot.axisFx({label: null, frameAnchor: "middle", dy: 10, facetAnchor: "empty"}),
+      Plot.frame({facetAnchor: "empty"})
+    ]
+  });
+}