Interactions: brush

README.md

@@ -1220,6 +1220,38 @@ Plot.vector(wind, {x: "longitude", y: "latitude", length: "speed", rotate: "dire
 
 Returns a new vector with the given *data* and *options*. If neither the **x** nor **y** options are specified, *data* is assumed to be an array of pairs [[*x₀*, *y₀*], [*x₁*, *y₁*], [*x₂*, *y₂*], …] such that **x** = [*x₀*, *x₁*, *x₂*, …] and **y** = [*y₀*, *y₁*, *y₂*, …].
 
+## Interactions
+
+Interactions are special marks that handle user input and define interactive selections. When a plot has an interaction mark, the returned *plot*.value represents the current selection as an array subset of the interaction mark’s data. As the user modifies the selection through interaction with the plot, *input* events are emitted. This design is compatible with [Observable’s viewof operator](https://observablehq.com/@observablehq/introduction-to-views), but you can also listen to *input* events directly via the [EventTarget interface](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget).
+
+### Brush
+
+[Source](./src/marks/brush.js) · [Examples](https://observablehq.com/@observablehq/plot-brush) · Selects points within a single contiguous rectangular region, such as nearby dots in a scatterplot.
+
+#### Plot.brush(*data*, *options*)
+
+```js
+Plot.brush(penguins, {x: "culmen_depth_mm", y: "culmen_length_mm"})
+```
+
+Returns a new brush with the given *data* and *options*. If neither the **x** nor **y** options are specified, *data* is assumed to be an array of pairs [[*x₀*, *y₀*], [*x₁*, *y₁*], [*x₂*, *y₂*], …] such that **x** = [*x₀*, *x₁*, *x₂*, …] and **y** = [*y₀*, *y₁*, *y₂*, …].
+
+#### Plot.brushX(*data*, *options*)
+
+```js
+Plot.brushX(penguins, {x: "culmen_depth_mm"})
+```
+
+Equivalent to [Plot.brush](#plotbrushdata-options) except that if the **x** option is not specified, it defaults to the identity function and assumes that *data* = [*x₀*, *x₁*, *x₂*, …].
+
+#### Plot.brushY(*data*, *options*)
+
+```js
+Plot.brushY(penguins, {y: "culmen_length_mm"})
+```
+
+Equivalent to [Plot.brush](#plotbrushdata-options) except that if the **y** option is not specified, it defaults to the identity function and assumes that *data* = [*y₀*, *y₁*, *y₂*, …].
+
 ## Decorations
 
 Decorations are static marks that do not represent data. Currently this includes only [Plot.frame](#frame), although internally Plot’s axes are implemented as decorations and may in the future be exposed here for more flexible configuration.

src/index.js

@@ -2,6 +2,7 @@ export {plot, Mark, marks} from "./plot.js";
 export {Area, area, areaX, areaY} from "./marks/area.js";
 export {Arrow, arrow} from "./marks/arrow.js";
 export {BarX, BarY, barX, barY} from "./marks/bar.js";
+export {brush, brushX, brushY} from "./marks/brush.js";
 export {Cell, cell, cellX, cellY} from "./marks/cell.js";
 export {Dot, dot, dotX, dotY} from "./marks/dot.js";
 export {Frame, frame} from "./marks/frame.js";
@@ -13,6 +14,7 @@ export {RuleX, RuleY, ruleX, ruleY} from "./marks/rule.js";
 export {Text, text, textX, textY} from "./marks/text.js";
 export {TickX, TickY, tickX, tickY} from "./marks/tick.js";
 export {Vector, vector} from "./marks/vector.js";
+export {selection} from "./selection.js";
 export {valueof} from "./options.js";
 export {filter, reverse, sort, shuffle} from "./transforms/basic.js";
 export {bin, binX, binY} from "./transforms/bin.js";

src/marks/brush.js

@@ -0,0 +1,87 @@
+import {brush as brusher, brushX as brusherX, brushY as brusherY, create, select} from "d3";
+import {identity, maybeTuple} from "../options.js";
+import {Mark} from "../plot.js";
+import {selection, selectionEquals} from "../selection.js";
+import {applyDirectStyles, applyIndirectStyles} from "../style.js";
+
+const defaults = {
+  ariaLabel: "brush",
+  fill: "#777",
+  fillOpacity: 0.3,
+  stroke: "#fff"
+};
+
+export class Brush extends Mark {
+  constructor(data, {x, y, ...options} = {}) {
+    super(
+      data,
+      [
+        {name: "x", value: x, scale: "x", optional: true},
+        {name: "y", value: y, scale: "y", optional: true}
+      ],
+      options,
+      defaults
+    );
+    this.activeElement = null;
+  }
+  render(index, {x, y}, {x: X, y: Y}, dimensions) {
+    const {ariaLabel, ariaDescription, ariaHidden, ...options} = this;
+    const {marginLeft, width, marginRight, marginTop, height, marginBottom} = dimensions;
+    const brush = this;
+    const g = create("svg:g")
+        .call(applyIndirectStyles, {ariaLabel, ariaDescription, ariaHidden})
+        .call((X && Y ? brusher : X ? brusherX : brusherY)()
+          .extent([[marginLeft, marginTop], [width - marginRight, height - marginBottom]])
+          .on("start brush end", function(event) {
+            const {type, selection: extent} = event;
+            // For faceting, when starting a brush in a new facet, clear the
+            // brush and selection on the old facet. In the future, we might
+            // allow independent brushes across facets by disabling this?
+            if (type === "start" && brush.activeElement !== this) {
+              if (brush.activeElement !== null) {
+                select(brush.activeElement).call(event.target.clear, event);
+                brush.activeElement[selection] = null;
+              }
+              brush.activeElement = this;
+            }
+            let S = null;
+            if (extent) {
+              S = index;
+              if (X) {
+                let [x0, x1] = Y ? [extent[0][0], extent[1][0]] : extent;
+                if (x.bandwidth) x0 -= x.bandwidth();
+                S = S.filter(i => x0 <= X[i] && X[i] <= x1);
+              }
+              if (Y) {
+                let [y0, y1] = X ? [extent[0][1], extent[1][1]] : extent;
+                if (y.bandwidth) y0 -= y.bandwidth();
+                S = S.filter(i => y0 <= Y[i] && Y[i] <= y1);
+              }
+            }
+            if (!selectionEquals(this[selection], S)) {
+              this[selection] = S;
+              this.dispatchEvent(new Event("input", {bubbles: true}));
+            }
+          }))
+        .call(g => g.selectAll(".selection")
+          .attr("shape-rendering", null) // reset d3-brush
+          .call(applyIndirectStyles, options)
+          .call(applyDirectStyles, options))
+      .node();
+    g[selection] = null;
+    return g;
+  }
+}
+
+export function brush(data, {x, y, ...options} = {}) {
+  ([x, y] = maybeTuple(x, y));
+  return new Brush(data, {...options, x, y});
+}
+
+export function brushX(data, {x = identity, ...options} = {}) {
+  return new Brush(data, {...options, x, y: null});
+}
+
+export function brushY(data, {y = identity, ...options} = {}) {
+  return new Brush(data, {...options, x: null, y});
+}

src/plot.js

@@ -1,11 +1,12 @@
-import {create, cross, difference, groups, InternMap} from "d3";
+import {create, cross, difference, groups, InternMap, union} from "d3";
 import {Axes, autoAxisTicks, autoScaleLabels} from "./axes.js";
 import {Channel, channelSort} from "./channel.js";
 import {defined} from "./defined.js";
 import {Dimensions} from "./dimensions.js";
 import {Legends, exposeLegends} from "./legends.js";
-import {arrayify, isOptions, keyword, range, first, second, where} from "./options.js";
+import {arrayify, isOptions, keyword, range, first, second, where, take} from "./options.js";
 import {Scales, ScaleFunctions, autoScaleRange, applyScales, exposeScales} from "./scales.js";
+import {selection} from "./selection.js";
 import {applyInlineStyles, maybeClassName, styles} from "./style.js";
 import {basic} from "./transforms/basic.js";
 
@@ -95,12 +96,21 @@ export function plot(options = {}) {
       .call(applyInlineStyles, style)
     .node();
 
+  let initialValue;
   for (const mark of marks) {
     const channels = markChannels.get(mark) ?? [];
     const values = applyScales(channels, scales);
     const index = filter(markIndex.get(mark), channels, values);
     const node = mark.render(index, scales, values, dimensions, axes);
-    if (node != null) svg.appendChild(node);
+    if (node != null) {
+      if (node[selection] !== undefined) {
+        initialValue = markValue(mark, node[selection]);
+        node.addEventListener("input", () => {
+          figure.value = markValue(mark, node[selection]);
+        });
+      }
+      svg.appendChild(node);
+    }
   }
 
   // Wrap the plot in a figure with a caption, if desired.
@@ -119,6 +129,7 @@ export function plot(options = {}) {
 
   figure.scale = exposeScales(scaleDescriptors);
   figure.legend = exposeLegends(scaleDescriptors, options);
+  figure.value = initialValue;
   return figure;
 }
 
@@ -189,6 +200,10 @@ function markify(mark) {
   return mark instanceof Mark ? mark : new Render(mark);
 }
 
+function markValue(mark, selection) {
+  return selection === null ? mark.data : take(mark.data, selection);
+}
+
 class Render extends Mark {
   constructor(render) {
     super();
@@ -263,16 +278,17 @@ class Facet extends Mark {
     }
     return {index, channels: [...channels, ...subchannels]};
   }
-  render(I, scales, channels, dimensions, axes) {
-    const {marks, marksChannels, marksIndexByFacet} = this;
+  render(I, scales, _, dimensions, axes) {
+    const {data, channels, marks, marksChannels, marksIndexByFacet} = this;
     const {fx, fy} = scales;
     const fyDomain = fy && fy.domain();
     const fxDomain = fx && fx.domain();
     const fyMargins = fy && {marginTop: 0, marginBottom: 0, height: fy.bandwidth()};
     const fxMargins = fx && {marginRight: 0, marginLeft: 0, width: fx.bandwidth()};
     const subdimensions = {...dimensions, ...fxMargins, ...fyMargins};
     const marksValues = marksChannels.map(channels => applyScales(channels, scales));
-    return create("svg:g")
+    let selectionByFacet;
+    const parent = create("svg:g")
         .call(g => {
           if (fy && axes.y) {
             const axis1 = axes.y, axis2 = nolabel(axis1);
@@ -316,10 +332,25 @@ class Facet extends Mark {
                 const values = marksValues[i];
                 const index = filter(marksFacetIndex[i], marksChannels[i], values);
                 const node = marks[i].render(index, scales, values, subdimensions);
-                if (node != null) this.appendChild(node);
+                if (node != null) {
+                  if (node[selection] !== undefined) {
+                    if (marks[i].data !== data) throw new Error("selection must use facet data");
+                    if (selectionByFacet === undefined) selectionByFacet = facetMap(channels);
+                    selectionByFacet.set(key, node[selection]);
+                    node.addEventListener("input", () => {
+                      selectionByFacet.set(key, node[selection]);
+                      parent[selection] = facetSelection(selectionByFacet);
+                    });
+                  }
+                  this.appendChild(node);
+                }
               }
             }))
       .node();
+    if (selectionByFacet !== undefined) {
+      parent[selection] = facetSelection(selectionByFacet);
+    }
+    return parent;
   }
 }
 
@@ -362,6 +393,20 @@ function facetTranslate(fx, fy) {
     : ky => `translate(0,${fy(ky)})`;
 }
 
+// If multiple facets define a selection, then the overall selection is the
+// union of the defined selections. As with non-faceted plots, we assume that
+// only a single mark is defining the selection; if multiple marks define a
+// selection, generally speaking the last one wins, although the behavior is not
+// explicitly defined.
+function facetSelection(selectionByFacet) {
+  let selection = null;
+  for (const value of selectionByFacet.values()) {
+    if (value === null) continue;
+    selection = selection === null ? value : union(selection, value);
+  }
+  return selection;
+}
+
 function facetMap(channels) {
   return new (channels.length > 1 ? FacetMap2 : FacetMap);
 }
@@ -379,6 +424,9 @@ class FacetMap {
   set(key, value) {
     return this._.set(key, value), this;
   }
+  values() {
+    return this._.values();
+  }
 }
 
 // A Map-like interface that supports paired keys.
@@ -397,4 +445,9 @@ class FacetMap2 extends FacetMap {
     else super.set(key1, new InternMap([[key2, value]]));
     return this;
   }
+  *values() {
+    for (const map of this._.values()) {
+      yield* map.values();
+    }
+  }
 }

src/selection.js

@@ -0,0 +1,18 @@
+// This symbol is used by interactive marks to define which data are selected. A
+// node returned by mark.render may expose a selection as node[selection], whose
+// value may be an array of numbers (e.g., [0, 1, 2, …]) representing an
+// in-order subset of the rendered index, or null if the selection is undefined.
+// The selection can be updated during interaction by emitting an input event.
+export const selection = Symbol("selection");
+
+// Given two (possibly null, possibly an index, but not undefined) selections,
+// returns true if the two represent the same selection, and false otherwise.
+// This assumes that the selection is a in-order subset of the original index.
+export function selectionEquals(s1, s2) {
+  if (s1 === s2) return true;
+  if (s1 == null || s2 == null) return false;
+  const n = s1.length;
+  if (n !== s2.length) return false;
+  for (let i = 0; i < n; ++i) if (s1[i] !== s2[i]) return false;
+  return true;
+}

src/style.js

@@ -32,7 +32,9 @@ export function styles(
   {
     ariaLabel: cariaLabel,
     fill: defaultFill = "currentColor",
+    fillOpacity: defaultFillOpacity,
     stroke: defaultStroke = "none",
+    strokeOpacity: defaultStrokeOpacity,
     strokeWidth: defaultStrokeWidth,
     strokeLinecap: defaultStrokeLinecap,
     strokeLinejoin: defaultStrokeLinejoin,
@@ -66,9 +68,9 @@ export function styles(
   }
 
   const [vfill, cfill] = maybeColorChannel(fill, defaultFill);
-  const [vfillOpacity, cfillOpacity] = maybeNumberChannel(fillOpacity);
+  const [vfillOpacity, cfillOpacity] = maybeNumberChannel(fillOpacity, defaultFillOpacity);
   const [vstroke, cstroke] = maybeColorChannel(stroke, defaultStroke);
-  const [vstrokeOpacity, cstrokeOpacity] = maybeNumberChannel(strokeOpacity);
+  const [vstrokeOpacity, cstrokeOpacity] = maybeNumberChannel(strokeOpacity, defaultStrokeOpacity);
   const [vopacity, copacity] = maybeNumberChannel(opacity);
 
   // For styles that have no effect if there is no stroke, only apply the

test/jsdom.js

@@ -19,6 +19,7 @@ function withJsdom(run) {
     const jsdom = new JSDOM("");
     global.window = jsdom.window;
     global.document = jsdom.window.document;
+    global.navigator = jsdom.window.navigator;
     global.Event = jsdom.window.Event;
     global.Node = jsdom.window.Node;
     global.NodeList = jsdom.window.NodeList;
@@ -29,6 +30,7 @@ function withJsdom(run) {
     } finally {
       delete global.window;
       delete global.document;
+      delete global.navigator;
       delete global.Event;
       delete global.Node;
       delete global.NodeList;