don’t coerce null percent to zero (#2073)

Author: mbostock

src/plot.js

@@ -403,7 +403,7 @@ function applyScaleTransform(channel, options) {
     type,
     percent,
     interval,
-    transform = percent ? (x) => x * 100 : maybeIntervalTransform(interval, type)
+    transform = percent ? (x) => (x == null ? NaN : x * 100) : maybeIntervalTransform(interval, type)
   } = options[scale] ?? {};
   if (transform == null) return;
   channel.value = map(channel.value, transform);

test/output/percentNull.svg

@@ -217,6 +217,7 @@ export * from "./penguin-species-island-sex.js";
 export * from "./penguin-species-island.js";
 export * from "./penguin-species.js";
 export * from "./penguin-voronoi-1d.js";
+export * from "./percent-null.js";
 export * from "./pointer-linked.js";
 export * from "./pointer.js";
 export * from "./polylinear.js";

test/plots/index.ts

@@ -0,0 +1,7 @@
+import * as Plot from "@observablehq/plot";
+
+export async function percentNull() {
+  const time = [1, 2, 3, 4, 5];
+  const value = [null, null, 1, null, null];
+  return Plot.dot(time, {x: time, y: value}).plot({y: {percent: true}});
+}