differenceX and shiftY (#1922)

* differenceX

* shiftY

* anchor

* consolidate DifferenceOptions

* update docs

* update test snapshots

* Update src/marks/difference.js

---------

Co-authored-by: Mike Bostock <mbostock@gmail.com>

docs/marks/difference.md

@@ -142,4 +142,12 @@ These options are passed to the underlying area and line marks; in particular, w
 Plot.differenceY(gistemp, {x: "Date", y: "Anomaly"})
 ```
 
-Returns a new difference with the given *data* and *options*. The mark is a composite of a positive area, negative area, and line. The positive area extends from the bottom of the frame to the line, and is clipped by the area extending from the comparison to the top of the frame. The negative area conversely extends from the top of the frame to the line, and is clipped by the area extending from the comparison to the bottom of the frame.
+Returns a new vertical difference with the given *data* and *options*. The mark is a composite of a positive area, negative area, and line. The positive area extends from the bottom of the frame to the line, and is clipped by the area extending from the comparison to the top of the frame. The negative area conversely extends from the top of the frame to the line, and is clipped by the area extending from the comparison to the bottom of the frame.
+
+## differenceX(*data*, *options*) <VersionBadge pr="1922" /> {#differenceX}
+
+```js
+Plot.differenceX(gistemp, {y: "Date", x: "Anomaly"})
+```
+
+Returns a new horizontal difference with the given *data* and *options*. See [differenceY](#differenceY) for more.

docs/transforms/shift.md

@@ -43,6 +43,16 @@ When looking at year-over-year growth, the chart is mostly green, implying that
 Plot.shiftX("7 days", {x: "Date", y: "Close"})
 ```
 
-Derives an **x1** channel from the input **x** channel by shifting values by the given *interval*. The *interval* may be specified as: a name (*second*, *minute*, *hour*, *day*, *week*, *month*, *quarter*, *half*, *year*, *monday*, *tuesday*, *wednesday*, *thursday*, *friday*, *saturday*, *sunday*) with an optional number and sign (*e.g.*, *+3 days* or *-1 year*); or as a number; or as an implementation — such as d3.utcMonth — with *interval*.floor(*value*), *interval*.offset(*value*), and *interval*.range(*start*, *stop*) methods.
+Derives an **x1** channel from the input **x** channel by shifting values by the given [*interval*](../features/intervals.md). The *interval* may be specified as: a name (*second*, *minute*, *hour*, *day*, *week*, *month*, *quarter*, *half*, *year*, *monday*, *tuesday*, *wednesday*, *thursday*, *friday*, *saturday*, *sunday*) with an optional number and sign (*e.g.*, *+3 days* or *-1 year*); or as a number; or as an implementation — such as d3.utcMonth — with *interval*.floor(*value*), *interval*.offset(*value*), and *interval*.range(*start*, *stop*) methods.
 
-The shiftX also transform aliases the **x** channel to **x2** and applies a domain hint to the **x2** channel such that by default the plot shows only the intersection of **x1** and **x2**. For example, if the interval is *+1 year*, the first year of the data is not shown.
+The shiftX transform also aliases the **x** channel to **x2** and applies a domain hint to the **x2** channel such that by default the plot shows only the intersection of **x1** and **x2**. For example, if the interval is *+1 year*, the first year of the data is not shown.
+
+## shiftY(*interval*, *options*) <VersionBadge pr="1922" /> {#shiftY}
+
+```js
+Plot.shiftY("7 days", {y: "Date", x: "Close"})
+```
+
+Derives a **y1** channel from the input **y** channel by shifting values by the given [*interval*](../features/intervals.md). See [shiftX](#shiftX) for more.
+
+The shiftY transform also aliases the **y** channel to **y2** and applies a domain hint to the **y2** channel such that by default the plot shows only the intersection of **y1** and **y2**. For example, if the interval is *+1 year*, the first year of the data is not shown.

src/index.js

@@ -20,7 +20,7 @@ export {Contour, contour} from "./marks/contour.js";
 export {crosshair, crosshairX, crosshairY} from "./marks/crosshair.js";
 export {delaunayLink, delaunayMesh, hull, voronoi, voronoiMesh} from "./marks/delaunay.js";
 export {Density, density} from "./marks/density.js";
-export {differenceY} from "./marks/difference.js";
+export {differenceX, differenceY} from "./marks/difference.js";
 export {Dot, dot, dotX, dotY, circle, hexagon} from "./marks/dot.js";
 export {Frame, frame} from "./marks/frame.js";
 export {Geo, geo, sphere, graticule} from "./marks/geo.js";
@@ -47,7 +47,7 @@ export {find, group, groupX, groupY, groupZ} from "./transforms/group.js";
 export {hexbin} from "./transforms/hexbin.js";
 export {normalize, normalizeX, normalizeY} from "./transforms/normalize.js";
 export {map, mapX, mapY} from "./transforms/map.js";
-export {shiftX} from "./transforms/shift.js";
+export {shiftX, shiftY} from "./transforms/shift.js";
 export {window, windowX, windowY} from "./transforms/window.js";
 export {select, selectFirst, selectLast, selectMaxX, selectMaxY, selectMinX, selectMinY} from "./transforms/select.js";
 export {stackX, stackX1, stackX2, stackY, stackY1, stackY2} from "./transforms/stack.js";

src/marks/difference.d.ts

@@ -6,7 +6,8 @@ import type {Data, MarkOptions, RenderableMark} from "../mark.js";
 export interface DifferenceOptions extends MarkOptions, CurveOptions {
   /**
    * The comparison horizontal position channel, typically bound to the *x*
-   * scale; if not specified, **x** is used.
+   * scale; if not specified, **x** is used. For differenceX, defaults to zero
+   * if only one *x* and *y* channel is specified.
    */
   x1?: ChannelValueSpec;
 
@@ -69,6 +70,19 @@ export interface DifferenceOptions extends MarkOptions, CurveOptions {
   z?: ChannelValue;
 }
 
+/**
+ * Returns a new horizontal difference mark for the given the specified *data*
+ * and *options*, as in a time-series chart where time goes down↓ (or up↑).
+ *
+ * The mark is a composite of a positive area, negative area, and line. The
+ * positive area extends from the left of the frame to the line, and is clipped
+ * by the area extending from the comparison to the right of the frame. The
+ * negative area conversely extends from the right of the frame to the line, and
+ * is clipped by the area extending from the comparison to the left of the
+ * frame.
+ */
+export function differenceX(data?: Data, options?: DifferenceOptions): Difference;
+
 /**
  * Returns a new vertical difference mark for the given the specified *data* and
  * *options*, as in a time-series chart where time goes right→ (or ←left).

src/marks/difference.js

@@ -6,15 +6,24 @@ import {getClipId} from "../style.js";
 import {area} from "./area.js";
 import {line} from "./line.js";
 
-export function differenceY(
+export function differenceX(data, options) {
+  return differenceK("x", data, options);
+}
+
+export function differenceY(data, options) {
+  return differenceK("y", data, options);
+}
+
+function differenceK(
+  k,
   data,
   {
     x1,
     x2,
     y1,
     y2,
-    x = x1 === undefined && x2 === undefined ? indexOf : undefined,
-    y = y1 === undefined && y2 === undefined ? identity : undefined,
+    x = x1 === undefined && x2 === undefined ? (k === "y" ? indexOf : identity) : undefined,
+    y = y1 === undefined && y2 === undefined ? (k === "x" ? indexOf : identity) : undefined,
     fill, // ignored
     positiveFill = "#3ca951",
     negativeFill = "#4269d0",
@@ -32,8 +41,11 @@ export function differenceY(
 ) {
   [x1, x2] = memoTuple(x, x1, x2);
   [y1, y2] = memoTuple(y, y1, y2);
-  if (x1 === x2 && y1 === y2) y1 = memo(0);
-  ({tip} = withTip({tip}, "x"));
+  if (x1 === x2 && y1 === y2) {
+    if (k === "y") y1 = memo(0);
+    else x1 = memo(0);
+  }
+  ({tip} = withTip({tip}, k === "y" ? "x" : "y"));
   return marks(
     !isNoneish(positiveFill)
       ? Object.assign(
@@ -45,7 +57,7 @@ export function differenceY(
             z,
             fill: positiveFill,
             fillOpacity: positiveFillOpacity,
-            render: composeRender(render, clipDifferenceY(true)),
+            render: composeRender(render, clipDifference(k, true)),
             clip,
             ...options
           }),
@@ -62,7 +74,7 @@ export function differenceY(
             z,
             fill: negativeFill,
             fillOpacity: negativeFillOpacity,
-            render: composeRender(render, clipDifferenceY(false)),
+            render: composeRender(render, clipDifference(k, false)),
             clip,
             ...options
           }),
@@ -110,15 +122,20 @@ function memo(v) {
   return {transform: (data) => V || (V = valueof(data, value)), label};
 }
 
-function clipDifferenceY(positive) {
+function clipDifference(k, positive) {
+  const f = k === "x" ? "y" : "x"; // f is the flipped dimension
+  const f1 = `${f}1`;
+  const f2 = `${f}2`;
+  const k1 = `${k}1`;
+  const k2 = `${k}2`;
   return (index, scales, channels, dimensions, context, next) => {
-    const {x1, x2} = channels;
-    const {height} = dimensions;
-    const y1 = new Float32Array(x1.length);
-    const y2 = new Float32Array(x2.length);
-    (positive === inferScaleOrder(scales.y) < 0 ? y1 : y2).fill(height);
-    const oc = next(index, scales, {...channels, x2: x1, y2}, dimensions, context);
-    const og = next(index, scales, {...channels, x1: x2, y1}, dimensions, context);
+    const {[f1]: F1, [f2]: F2} = channels;
+    const K1 = new Float32Array(F1.length);
+    const K2 = new Float32Array(F2.length);
+    const m = dimensions[k === "y" ? "height" : "width"];
+    (positive === inferScaleOrder(scales[k]) < 0 ? K1 : K2).fill(m);
+    const oc = next(index, scales, {...channels, [f2]: F1, [k2]: K2}, dimensions, context);
+    const og = next(index, scales, {...channels, [f1]: F2, [k1]: K1}, dimensions, context);
     const c = oc.querySelector("g") ?? oc; // applyClip
     const g = og.querySelector("g") ?? og; // applyClip
     for (let i = 0; c.firstChild; i += 2) {

src/transforms/shift.d.ts

@@ -7,3 +7,10 @@ import type {Transformed} from "./basic.js";
  * *x* channel according to the specified *interval*.
  */
 export function shiftX<T>(interval: Interval, options?: T): Transformed<T>;
+
+/**
+ * Groups data into series using the first channel of *z*, *fill*, or *stroke*
+ * (if any), then derives *y1* and *y2* output channels by shifting the input
+ * *y* channel according to the specified *interval*.
+ */
+export function shiftY<T>(interval: Interval, options?: T): Transformed<T>;

src/transforms/shift.js

@@ -7,6 +7,10 @@ export function shiftX(interval, options) {
   return shiftK("x", interval, options);
 }
 
+export function shiftY(interval, options) {
+  return shiftK("y", interval, options);
+}
+
 function shiftK(x, interval, options = {}) {
   let offset;
   let k = 1;