improve bin type coercion (#790)

Author: mbostock

src/transforms/bin.js

@@ -1,6 +1,6 @@
 import {bin as binner, extent, thresholdFreedmanDiaconis, thresholdScott, thresholdSturges, utcTickInterval} from "d3";
 import {valueof, range, identity, maybeLazyChannel, maybeTuple, maybeColorChannel, maybeValue, mid, labelof, isTemporal} from "../options.js";
-import {coerceDate} from "../scales.js";
+import {coerceDate, coerceNumber} from "../scales.js";
 import {basic} from "./basic.js";
 import {hasOutput, maybeEvaluator, maybeGroup, maybeOutput, maybeOutputs, maybeReduce, maybeSort, maybeSubgroup, reduceCount, reduceIdentity} from "./group.js";
 import {maybeInsetX, maybeInsetY} from "./inset.js";
@@ -181,7 +181,7 @@ function maybeBin(options) {
   if (options == null) return;
   const {value, cumulative, domain = extent, thresholds} = options;
   const bin = data => {
-    let V = valueof(data, value);
+    let V = valueof(data, value, Array); // d3.bin prefers Array input
     const bin = binner().value(i => V[i]);
     if (isTemporal(V) || isTimeThresholds(thresholds)) {
       V = V.map(coerceDate);
@@ -197,6 +197,7 @@ function maybeBin(options) {
       }
       bin.thresholds(t).domain([min, max]);
     } else {
+      V = V.map(coerceNumber);
       let d = domain;
       let t = thresholds;
       if (isInterval(t)) {

test/output/binStrings.svg

@@ -0,0 +1,5 @@
+import * as Plot from "@observablehq/plot";
+
+export default async function() {
+  return Plot.rectY(["9.6", "9.6", "14.8", "14.8", "7.2"], Plot.binX()).plot();
+}

test/output/binTimestamps.svg

@@ -0,0 +1,7 @@
+import * as Plot from "@observablehq/plot";
+import * as d3 from "d3";
+
+export default async function() {
+  const timestamps = Float64Array.of(1609459200000, 1609545600000, 1609632000000, 1609718400000, 1609804800000, 1609891200000, 1609977600000);
+  return Plot.rectY(timestamps, Plot.binX({y: "count"}, {interval: d3.utcDay})).plot();
+}

test/output/stringBins.svg

@@ -23,6 +23,8 @@ export {default as athletesWeightCumulative} from "./athletes-weight-cumulative.
 export {default as availability} from "./availability.js";
 export {default as ballotStatusRace} from "./ballot-status-race.js";
 export {default as beckerBarley} from "./becker-barley.js";
+export {default as binStrings} from "./bin-strings.js";
+export {default as binTimestamps} from "./bin-timestamps.js";
 export {default as boxplot} from "./boxplot.js";
 export {default as caltrain} from "./caltrain.js";
 export {default as caltrainDirection} from "./caltrain-direction.js";