reindex symbol

Author: mbostock

src/options.js

@@ -7,6 +7,10 @@ import {maybeTimeInterval, maybeUtcInterval} from "./time.js";
 export const TypedArray = Object.getPrototypeOf(Uint8Array);
 const objectToString = Object.prototype.toString;
 
+// If a reindex is attached to the data, channel values expressed as arrays will
+// be reindexed when the channels are instantiated. See exclusiveFacets.
+export const reindex = Symbol("reindex");
+
 export function valueof(data, value, type) {
   const valueType = typeof value;
   return valueType === "string"
@@ -17,7 +21,7 @@ export function valueof(data, value, type) {
     ? map(data, constant(value), type)
     : typeof value?.transform === "function"
     ? maybeTypedArrayify(value.transform(data), type)
-    : maybeTake(maybeTypedArrayify(value, type), data?.reindex);
+    : maybeTake(maybeTypedArrayify(value, type), data?.[reindex]);
 }
 
 function maybeTake(values, index) {

src/transforms/exclusiveFacets.js

@@ -1,4 +1,4 @@
-import {slice} from "../options.js";
+import {reindex, slice} from "../options.js";
 
 export function exclusiveFacets(data, facets) {
   if (facets.length === 1) return {data, facets}; // only one facet; trivially exclusive
@@ -20,18 +20,18 @@ export function exclusiveFacets(data, facets) {
 
   // For each overlapping index (duplicate), assign a new unique index at the
   // end of the existing array, duplicating the datum. For example, [[0, 1, 2],
-  // [2, 1, 3]] would become [[0, 1, 2], [4, 5, 3]].
+  // [2, 1, 3]] would become [[0, 1, 2], [4, 5, 3]]. Also attach a reindex to
+  // the data to preserve the association of channel values specified as arrays.
   data = slice(data);
-  // Attach a reindex map to the data, to interpret channels specified as arrays.
-  data.reindex = new Uint32Array(n + overlaps);
+  const R = (data[reindex] = new Uint32Array(n + overlaps));
   facets = facets.map((facet) => slice(facet, Uint32Array));
   let j = n;
   O.fill(0);
   for (const facet of facets) {
     for (let k = 0, m = facet.length; k < m; ++k) {
       const i = facet[k];
-      if (O[i]) (facet[k] = j), (data[j] = data[i]), (data.reindex[j] = i), ++j;
-      else data.reindex[i] = i;
+      if (O[i]) (facet[k] = j), (data[j] = data[i]), (R[j] = i), ++j;
+      else R[i] = i;
       O[i] = 1;
     }
   }