ordinal time axis

src/marks/axis.js

@@ -1,13 +1,13 @@
-import {extent, format, timeFormat, utcFormat} from "d3";
+import {extent, format, median, pairs, timeFormat, utcFormat} from "d3";
 import {formatDefault} from "../format.js";
 import {marks} from "../mark.js";
 import {radians} from "../math.js";
 import {arrayify, constant, identity, keyword, number, range, valueof} from "../options.js";
-import {isIterable, isNoneish, isTemporal, orderof} from "../options.js";
+import {isIterable, isNoneish, isTemporal, isTimeInterval, orderof} from "../options.js";
 import {maybeColorChannel, maybeNumberChannel, maybeRangeInterval} from "../options.js";
-import {isTemporalScale} from "../scales.js";
+import {isOrdinalScale, isTemporalScale} from "../scales.js";
 import {offset} from "../style.js";
-import {formatTimeTicks, isTimeYear, isUtcYear} from "../time.js";
+import {formatTimeInterval, formatTimeTicks, inferTimeFormat, isTimeYear, isUtcYear} from "../time.js";
 import {initializer} from "../transforms/basic.js";
 import {ruleX, ruleY} from "./rule.js";
 import {text, textX, textY} from "./text.js";
@@ -277,7 +277,7 @@ function axisTickKy(
     ...options
   }
 ) {
-  return axisMark(vectorY, k, `${k}-axis tick`, data, {
+  return axisMark(vectorY, k, anchor, `${k}-axis tick`, data, {
     strokeWidth,
     strokeLinecap,
     strokeLinejoin,
@@ -311,7 +311,7 @@ function axisTickKx(
     ...options
   }
 ) {
-  return axisMark(vectorX, k, `${k}-axis tick`, data, {
+  return axisMark(vectorX, k, anchor, `${k}-axis tick`, data, {
     strokeWidth,
     strokeLinejoin,
     strokeLinecap,
@@ -336,8 +336,7 @@ function axisTextKy(
     tickSize,
     tickRotate = 0,
     tickPadding = Math.max(3, 9 - tickSize) + (Math.abs(tickRotate) > 60 ? 4 * Math.cos(tickRotate * radians) : 0),
-    tickFormat,
-    text = typeof tickFormat === "function" ? tickFormat : undefined,
+    text,
     textAnchor = Math.abs(tickRotate) > 60 ? "middle" : anchor === "left" ? "end" : "start",
     lineAnchor = tickRotate > 60 ? "top" : tickRotate < -60 ? "bottom" : "middle",
     fontVariant,
@@ -352,12 +351,13 @@ function axisTextKy(
   return axisMark(
     textY,
     k,
+    anchor,
     `${k}-axis tick label`,
     data,
     {
       facetAnchor,
       frameAnchor,
-      text: text === undefined ? null : text,
+      text,
       textAnchor,
       lineAnchor,
       fontVariant,
@@ -366,7 +366,7 @@ function axisTextKy(
       ...options,
       dx: anchor === "left" ? +dx - tickSize - tickPadding + +insetLeft : +dx + +tickSize + +tickPadding - insetRight
     },
-    function (scale, data, ticks, channels) {
+    function (scale, data, ticks, tickFormat, channels) {
       if (fontVariant === undefined) this.fontVariant = inferFontVariant(scale);
       if (text === undefined) channels.text = inferTextChannel(scale, data, ticks, tickFormat, anchor);
     }
@@ -383,8 +383,7 @@ function axisTextKx(
     tickSize,
     tickRotate = 0,
     tickPadding = Math.max(3, 9 - tickSize) + (Math.abs(tickRotate) >= 10 ? 4 * Math.cos(tickRotate * radians) : 0),
-    tickFormat,
-    text = typeof tickFormat === "function" ? tickFormat : undefined,
+    text,
     textAnchor = Math.abs(tickRotate) >= 10 ? ((tickRotate < 0) ^ (anchor === "bottom") ? "start" : "end") : "middle",
     lineAnchor = Math.abs(tickRotate) >= 10 ? "middle" : anchor === "bottom" ? "top" : "bottom",
     fontVariant,
@@ -399,6 +398,7 @@ function axisTextKx(
   return axisMark(
     textX,
     k,
+    anchor,
     `${k}-axis tick label`,
     data,
     {
@@ -413,7 +413,7 @@ function axisTextKx(
       ...options,
       dy: anchor === "bottom" ? +dy + +tickSize + +tickPadding - insetBottom : +dy - tickSize - tickPadding + +insetTop
     },
-    function (scale, data, ticks, channels) {
+    function (scale, data, ticks, tickFormat, channels) {
       if (fontVariant === undefined) this.fontVariant = inferFontVariant(scale);
       if (text === undefined) channels.text = inferTextChannel(scale, data, ticks, tickFormat, anchor);
     }
@@ -452,7 +452,7 @@ function gridKy(
     ...options
   }
 ) {
-  return axisMark(ruleY, k, `${k}-grid`, data, {y, x1, x2, ...gridDefaults(options)});
+  return axisMark(ruleY, k, anchor, `${k}-grid`, data, {y, x1, x2, ...gridDefaults(options)});
 }
 
 function gridKx(
@@ -467,7 +467,7 @@ function gridKx(
     ...options
   }
 ) {
-  return axisMark(ruleX, k, `${k}-grid`, data, {x, y1, y2, ...gridDefaults(options)});
+  return axisMark(ruleX, k, anchor, `${k}-grid`, data, {x, y1, y2, ...gridDefaults(options)});
 }
 
 function gridDefaults({
@@ -517,15 +517,17 @@ function labelOptions(
   };
 }
 
-function axisMark(mark, k, ariaLabel, data, options, initialize) {
+function axisMark(mark, k, anchor, ariaLabel, data, options, initialize) {
   let channels;
 
   function axisInitializer(data, facets, _channels, scales, dimensions, context) {
     const initializeFacets = data == null && (k === "fx" || k === "fy");
     const {[k]: scale} = scales;
     if (!scale) throw new Error(`missing scale: ${k}`);
-    let {ticks, tickSpacing, interval} = options;
-    if (isTemporalScale(scale) && typeof ticks === "string") (interval = ticks), (ticks = undefined);
+    let {ticks, tickFormat, interval} = options;
+    // TODO what if ticks is a time interval implementation?
+    // TODO allow ticks to be a function?
+    if (hasTimeTicks(scale) && typeof ticks === "string") (interval = ticks), (ticks = undefined);
     if (data == null) {
       if (isIterable(ticks)) {
         data = arrayify(ticks);
@@ -542,21 +544,38 @@ function axisMark(mark, k, ariaLabel, data, options, initialize) {
             const [min, max] = extent(scale.domain());
             data = interval.range(min, interval.offset(interval.floor(max))); // inclusive max
           } else {
-            const [min, max] = extent(scale.range());
-            ticks = (max - min) / (tickSpacing === undefined ? (k === "x" ? 80 : 35) : tickSpacing);
+            ticks = inferTickCount(k, scale, options);
             data = scale.ticks(ticks);
           }
         }
       } else {
         data = scale.domain();
+        if (isTimeInterval(scale.interval)) {
+          const type = "utc"; // TODO infer type of ordinal time
+          const [start, stop] = extent(data);
+          if (interval !== undefined) data = maybeRangeInterval(interval, type).range(start, +stop + 1); // inclusive stop
+          if (ticks === undefined) ticks = inferTickCount(k, scale, options);
+          const n = Math.max(1, getSkip(data, ticks));
+          const s = getMedianStep(data);
+          const f = inferTimeFormat(s * n);
+          const [i, I] = f;
+          // const [j, J] = inferTimeFormat(s);
+          data = maybeRangeInterval(I, type).range(start, +stop + 1); // inclusive stop
+          // TODO check if isSubsumingInterval(interval, data)
+          if (tickFormat === undefined) {
+            const format = utcFormat; // TODO based on type
+            const template = (f1, f2) => `${f1}\n${f2}`; // TODO based on anchor
+            tickFormat = formatTimeInterval(i, format, template);
+          }
+        }
       }
       if (k === "y" || k === "x") {
         facets = [range(data)];
       } else {
         channels[k] = {scale: k, value: identity};
       }
     }
-    initialize?.call(this, scale, data, ticks, channels);
+    initialize?.call(this, scale, data, ticks, tickFormat, channels);
     const initializedChannels = Object.fromEntries(
       Object.entries(channels).map(([name, channel]) => {
         return [name, {...channel, value: valueof(data, channel.value)}];
@@ -580,8 +599,34 @@ function axisMark(mark, k, ariaLabel, data, options, initialize) {
   return m;
 }
 
+// Compute the positive number n such that taking every nth value from the
+// scale’s domain produces as close as possible to the desired number of ticks.
+// For example, if the domain has 100 values and 5 ticks are desired, n = 20.
+function getSkip(domain, ticks) {
+  return domain.length / ticks;
+}
+
+// Compute the median step s between adjacent values from the scale’s domain.
+function getMedianStep(domain) {
+  return median(pairs(domain, (a, b) => Math.abs(b - a) || NaN));
+}
+
+function inferTickCount(k, scale, options) {
+  const {tickSpacing = k === "x" ? 80 : 35} = options;
+  const [min, max] = extent(scale.range());
+  return (max - min) / tickSpacing;
+}
+
+// Returns true if the given interval subsumes (i.e., covers, is
+// capable of generating) all of the specified values.
+// function isSubsumingInterval(interval, values) {
+//   return values.every((v) => interval.floor(v) >= v);
+// }
+
 function inferTextChannel(scale, data, ticks, tickFormat, anchor) {
-  return {value: inferTickFormat(scale, data, ticks, tickFormat, anchor)};
+  return {
+    value: typeof tickFormat === "function" ? tickFormat : inferTickFormat(scale, data, ticks, tickFormat, anchor)
+  };
 }
 
 // D3’s ordinal scales simply use toString by default, but if the ordinal scale
@@ -647,7 +692,7 @@ function inferScaleOrder(scale) {
 // Takes the scale label, and if this is not an ordinal scale and the label was
 // inferred from an associated channel, adds an orientation-appropriate arrow.
 function formatAxisLabel(k, scale, {anchor, label = scale.label, labelAnchor, labelArrow} = {}) {
-  if (label == null || (label.inferred && isTemporalish(scale) && /^(date|time|year)$/i.test(label))) return;
+  if (label == null || (label.inferred && hasTimeTicks(scale) && /^(date|time|year)$/i.test(label))) return;
   label = String(label); // coerce to a string after checking if inferred
   if (labelArrow === "auto") labelArrow = (!scale.bandwidth || scale.interval) && !/[↑↓→←]/.test(label);
   if (!labelArrow) return label;
@@ -684,6 +729,6 @@ function maybeLabelArrow(labelArrow = "auto") {
     : keyword(labelArrow, "labelArrow", ["auto", "up", "right", "down", "left"]);
 }
 
-function isTemporalish(scale) {
-  return isTemporalScale(scale) || scale.interval != null;
+function hasTimeTicks(scale) {
+  return isTemporalScale(scale) || (isOrdinalScale(scale) && isTimeInterval(scale.interval));
 }

src/options.js

@@ -348,6 +348,14 @@ export function maybeNiceInterval(interval, type) {
   return interval;
 }
 
+export function isTimeInterval(t) {
+  return isInterval(t) && typeof t?.floor === "function" && t.floor() instanceof Date;
+}
+
+export function isInterval(t) {
+  return typeof t?.range === "function";
+}
+
 // This distinguishes between per-dimension options and a standalone value.
 export function maybeValue(value) {
   return value === undefined || isOptions(value) ? value : {value};

src/time.js

@@ -1,4 +1,4 @@
-import {bisector, extent, median, pairs, timeFormat, utcFormat} from "d3";
+import {bisector, extent, median, pairs, tickStep, timeFormat, utcFormat} from "d3";
 import {utcSecond, utcMinute, utcHour, unixDay, utcWeek, utcMonth, utcYear} from "d3";
 import {utcMonday, utcTuesday, utcWednesday, utcThursday, utcFriday, utcSaturday, utcSunday} from "d3";
 import {timeSecond, timeMinute, timeHour, timeDay, timeWeek, timeMonth, timeYear} from "d3";
@@ -12,22 +12,25 @@ const durationDay = durationHour * 24;
 const durationWeek = durationDay * 7;
 const durationMonth = durationDay * 30;
 const durationYear = durationDay * 365;
+const durationMin = Math.exp((Math.log(500) + Math.log(durationSecond)) / 2);
+const durationMax = Math.exp((Math.log(6 * durationMonth) + Math.log(durationYear)) / 2);
 
+// [format, interval, step]; year and millisecond are handled dynamically
 // See https://github.com/d3/d3-time/blob/9e8dc940f38f78d7588aad68a54a25b1f0c2d97b/src/ticks.js#L14-L33
 const formats = [
-  ["millisecond", 0.5 * durationSecond],
-  ["second", durationSecond],
-  ["second", 30 * durationSecond],
-  ["minute", durationMinute],
-  ["minute", 30 * durationMinute],
-  ["hour", durationHour],
-  ["hour", 12 * durationHour],
-  ["day", durationDay],
-  ["day", 2 * durationDay],
-  ["week", durationWeek],
-  ["month", durationMonth],
-  ["month", 3 * durationMonth],
-  ["year", durationYear]
+  ["second", "1 second", durationSecond],
+  ["second", "30 seconds", 30 * durationSecond],
+  ["minute", "1 minute", durationMinute],
+  ["minute", "30 minutes", 30 * durationMinute],
+  ["hour", "1 hour", durationHour],
+  ["hour", "12 hours", 12 * durationHour],
+  ["day", "1 day", durationDay],
+  ["day", "2 days", 2 * durationDay],
+  ["week", "1 week", durationWeek],
+  ["week", "2 weeks", 2 * durationWeek],
+  ["month", "1 month", durationMonth],
+  ["month", "3 months", 3 * durationMonth],
+  ["month", "6 months", 6 * durationMonth] // https://github.com/d3/d3-time/issues/46
 ];
 
 const timeIntervals = new Map([
@@ -110,15 +113,31 @@ export function isTimeYear(i) {
   return timeYear(date) >= date; // coercing equality
 }
 
+// Compute the median difference between adjacent ticks, ignoring repeated
+// ticks; this implies an effective time interval, assuming that ticks are
+// regularly spaced; choose the largest format less than this interval so that
+// the ticks show the field that is changing. If the ticks are not available,
+// fallback to an approximation based on the desired number of ticks.
 export function formatTimeTicks(scale, data, ticks, anchor) {
-  const format = scale.type === "time" ? timeFormat : utcFormat;
-  const template =
+  let step = median(pairs(data, (a, b) => Math.abs(b - a) || NaN));
+  if (!(step > 0)) {
+    const [start, stop] = extent(scale.domain());
+    const count = typeof ticks === "number" ? ticks : 10;
+    step = Math.abs(stop - start) / count;
+  }
+  return formatTimeInterval(
+    inferTimeFormat(step)[0],
+    scale.type === "time" ? timeFormat : utcFormat,
     anchor === "left" || anchor === "right"
       ? (f1, f2) => `\n${f1}\n${f2}` // extra newline to keep f1 centered
       : anchor === "top"
       ? (f1, f2) => `${f2}\n${f1}`
-      : (f1, f2) => `${f1}\n${f2}`;
-  switch (getTimeTicksInterval(scale, data, ticks)) {
+      : (f1, f2) => `${f1}\n${f2}`
+  );
+}
+
+export function formatTimeInterval(interval, format, template) {
+  switch (interval) {
     case "millisecond":
       return formatConditional(format(".%L"), format(":%M:%S"), template);
     case "second":
@@ -139,18 +158,14 @@ export function formatTimeTicks(scale, data, ticks, anchor) {
   throw new Error("unable to format time ticks");
 }
 
-// Compute the median difference between adjacent ticks, ignoring repeated
-// ticks; this implies an effective time interval, assuming that ticks are
-// regularly spaced; choose the largest format less than this interval so that
-// the ticks show the field that is changing. If the ticks are not available,
-// fallback to an approximation based on the desired number of ticks.
-function getTimeTicksInterval(scale, data, ticks) {
-  const medianStep = median(pairs(data, (a, b) => Math.abs(b - a) || NaN));
-  if (medianStep > 0) return formats[bisector(([, step]) => step).right(formats, medianStep, 1, formats.length) - 1][0];
-  const [start, stop] = extent(scale.domain());
-  const count = typeof ticks === "number" ? ticks : 10;
-  const step = Math.abs(stop - start) / count;
-  return formats[bisector(([, step]) => Math.log(step)).center(formats, Math.log(step))][0];
+// Use the median step s to determine the standard time interval i that is
+// closest to the median step s times n (per 1). For example, if the scale’s
+// interval is day and n = 20, then i = month; if the scale’s interval is day
+// and n = 7, then i = week.
+export function inferTimeFormat(s) {
+  if (s < durationMin) return (s = tickStep(0, s, 1)), ["millisecond", `${s} milliseconds`, s];
+  if (s > durationMax) return (s = tickStep(0, s / durationYear, 1)), ["year", `${s} years`, s * durationYear];
+  return formats[bisector(([, , step]) => Math.log(step)).center(formats, Math.log(s))];
 }
 
 function formatConditional(format1, format2, template) {

src/transforms/bin.js

@@ -13,8 +13,10 @@ import {
   coerceDate,
   coerceNumbers,
   identity,
+  isInterval,
   isIterable,
   isTemporal,
+  isTimeInterval,
   labelof,
   map,
   maybeApplyInterval,
@@ -361,14 +363,6 @@ function isTimeThresholds(t) {
   return isTimeInterval(t) || (isIterable(t) && isTemporal(t));
 }
 
-function isTimeInterval(t) {
-  return isInterval(t) && typeof t === "function" && t() instanceof Date;
-}
-
-function isInterval(t) {
-  return typeof t?.range === "function";
-}
-
 function bing(EX, EY) {
   return EX && EY
     ? function* (I) {