Auto mark

src/index.js

@@ -2,6 +2,7 @@ export {plot} from "./plot.js";
 export {Mark, marks} from "./mark.js";
 export {Area, area, areaX, areaY} from "./marks/area.js";
 export {Arrow, arrow} from "./marks/arrow.js";
+export {auto} from "./marks/auto.js";
 export {axisX, axisY, axisFx, axisFy, gridX, gridY, gridFx, gridFy} from "./marks/axis.js";
 export {BarX, BarY, barX, barY} from "./marks/bar.js";
 export {boxX, boxY} from "./marks/box.js";

src/marks/auto.js

@@ -0,0 +1,274 @@
+import {InternSet} from "d3";
+import {isOrdinal, labelof, valueof, isOptions, isColor} from "../options.js";
+import {area, areaX, areaY} from "./area.js";
+import {dot} from "./dot.js";
+import {line, lineX, lineY} from "./line.js";
+import {ruleX, ruleY} from "./rule.js";
+import {barX, barY} from "./bar.js";
+import {rect, rectX, rectY} from "./rect.js";
+import {cell} from "./cell.js";
+import {frame} from "./frame.js";
+import {bin, binX, binY} from "../transforms/bin.js";
+import {group, groupX, groupY} from "../transforms/group.js";
+import {marks} from "../mark.js";
+import {ascending} from "d3";
+
+export function auto(data, {x, y, color, size, fx, fy, mark} = {}) {
+  // Allow x and y and other dimensions to be specified as shorthand field names
+  // (but note that they can also be specified as a {transform} object such as
+  // Plot.identity).
+  if (!isOptions(x)) x = makeOptions(x);
+  if (!isOptions(y)) y = makeOptions(y);
+  if (!isOptions(color)) color = isColor(color) ? {color} : makeOptions(color);
+  if (!isOptions(size)) size = makeOptions(size);
+
+  // We don’t apply any type inference to the fx and fy channels, if present, so
+  // these are simply passed-through to the underlying mark’s options.
+  if (isOptions(fx)) ({value: fx} = makeOptions(fx));
+  if (isOptions(fy)) ({value: fy} = makeOptions(fy));
+
+  const {value: xValue} = x;
+  const {value: yValue} = y;
+  const {value: sizeValue} = size;
+  const {value: colorValue, color: colorColor} = color;
+
+  // Determine the default reducer, if any.
+  let {reduce: xReduce} = x;
+  let {reduce: yReduce} = y;
+  let {reduce: sizeReduce} = size;
+  let {reduce: colorReduce} = color;
+  if (xReduce === undefined)
+    xReduce = yReduce == null && xValue == null && sizeValue == null && yValue != null ? "count" : null;
+  if (yReduce === undefined)
+    yReduce = xReduce == null && yValue == null && sizeValue == null && xValue != null ? "count" : null;
+
+  let {zero: xZero} = x;
+  let {zero: yZero} = y;
+
+  // TODO The line mark will need z?
+  // TODO Limit and sort for bar charts (e.g. alphabet)?
+  // TODO Look at Plot warnings and see how many we can prevent
+  // TODO Default to something other than turbo for continuous? Like:
+  //      scheme: (colorValue && isContinuous(color)) || colorReduce ? "ylgnbu" : undefined
+
+  // To apply heuristics based on the data types (values), realize the columns.
+  // We could maybe look at the data.schema here, but Plot’s behavior depends on
+  // the actual values anyway, so this probably is what we want. By
+  // materializing the columns here, we also ensure that they aren’t re-computed
+  // later in Plot.plot.
+  x = valueof(data, xValue);
+  y = valueof(data, yValue);
+  color = valueof(data, colorValue);
+  size = valueof(data, sizeValue);
+
+  // TODO Shorthand: array of primitives should result in a histogram
+  if (!x && !y) throw new Error("must specify x or y");
+  if (xReduce != null && !y) throw new Error("reducing x requires y");
+  if (yReduce != null && !x) throw new Error("reducing y requires x");
+
+  let z, zReduce;
+
+  // Propagate the x and y labels (field names), if any. This is necessary for
+  // any column we materialize (and hence, we don’t need to do this for fx and
+  // fy, since those columns are not needed for type inference and hence are not
+  // greedily materialized).
+  if (x) x.label = labelof(xValue);
+  if (y) y.label = labelof(yValue);
+  if (color) color.label = labelof(colorValue);
+  if (size) size.label = labelof(sizeValue);
+
+  // Determine the default size reducer, if any.
+  if (
+    sizeReduce === undefined &&
+    sizeValue == null &&
+    colorReduce == null &&
+    xReduce == null &&
+    yReduce == null &&
+    (!x || isOrdinal(x)) &&
+    (!y || isOrdinal(y))
+  ) {
+    sizeReduce = "count";
+  }
+
+  // Determine the default mark type.
+  if (mark === undefined) {
+    mark =
+      sizeValue != null || sizeReduce != null
+        ? "dot"
+        : xReduce != null || yReduce != null || colorReduce != null
+        ? "bar"
+        : x && y
+        ? isContinuous(x) && isContinuous(y) && (isMonotonic(x) || isMonotonic(y))
+          ? "line"
+          : (isContinuous(x) && xZero) || (isContinuous(y) && yZero)
+          ? "bar"
+          : "dot"
+        : x
+        ? "rule"
+        : y
+        ? "rule"
+        : null;
+  }
+
+  let colorMode; // "fill" or "stroke"
+
+  // Determine the mark implementation.
+  if (mark != null) {
+    switch (`${mark}`.toLowerCase()) {
+      case "dot":
+        mark = dot;
+        colorMode = "stroke";
+        break;
+      case "line":
+        mark = x && y ? line : x ? lineX : lineY; // 1d line by index
+        colorMode = "stroke";
+        if (isHighCardinality(color)) z = null; // TODO only if z not set by user
+        break;
+      case "area":
+        mark =
+          x && y
+            ? isContinuous(x) && isMonotonic(x)
+              ? areaY
+              : isContinuous(y) && isMonotonic(y)
+              ? areaX
+              : area // TODO error? how does it work with ordinal?
+            : x
+            ? areaX
+            : areaY; // 1d area by index
+        colorMode = "fill";
+        if (isHighCardinality(color)) z = null; // TODO only if z not set by user
+        break;
+      case "rule":
+        mark = x ? ruleX : ruleY;
+        colorMode = "stroke";
+        break;
+      case "bar":
+        mark =
+          yReduce != null
+            ? isOrdinal(x)
+              ? barY
+              : rectY
+            : xReduce != null
+            ? isOrdinal(y)
+              ? barX
+              : rectX
+            : colorReduce != null
+            ? x && y && isOrdinal(x) && isOrdinal(y)
+              ? cell
+              : x && isOrdinal(x)
+              ? barY
+              : y && isOrdinal(y)
+              ? barX
+              : rect
+            : x && y && isOrdinal(x) && isOrdinal(y)
+            ? cell
+            : y && isOrdinal(y)
+            ? barX
+            : barY;
+        colorMode = "fill";
+        break;
+      default:
+        throw new Error(`invalid mark: ${mark}`);
+    }
+  }
+
+  // Determine the mark options.
+  let options = {x, y, [colorMode]: color ?? colorColor, z, r: size, fx, fy};
+  let transform;
+  let transformOptions = {[colorMode]: colorReduce, z: zReduce, r: sizeReduce};
+  if (xReduce != null && yReduce != null) {
+    throw new Error(`cannot reduce both x and y`); // for now at least
+  } else if (yReduce != null) {
+    transformOptions.y = yReduce;
+    transform = isOrdinal(x) ? groupX : binX;
+  } else if (xReduce != null) {
+    transformOptions.x = xReduce;
+    transform = isOrdinal(y) ? groupY : binY;
+  } else if (colorReduce != null || sizeReduce != null) {
+    if (x && y) {
+      transform = isOrdinal(x) && isOrdinal(y) ? group : isOrdinal(x) ? binY : isOrdinal(y) ? binX : bin;
+    } else if (x) {
+      transform = isOrdinal(x) ? groupX : binX;
+    } else if (y) {
+      transform = isOrdinal(y) ? groupY : binY;
+    }
+  }
+  if (transform) options = transform(transformOptions, options);
+
+  // If zero-ness is not specified, default based on whether the resolved mark
+  // type will include a zero baseline.
+  if (xZero === undefined) xZero = transform !== binX && (mark === barX || mark === areaX || mark === rectX);
+  if (yZero === undefined) yZero = transform !== binY && (mark === barY || mark === areaY || mark === rectY);
+
+  // In the case of filled marks (particularly bars and areas) the frame and
+  // rules should come after the mark; in the case of stroked marks
+  // (particularly dots and lines) they should come before the mark.
+  const frames = fx != null || fy != null ? frame({strokeOpacity: 0.1}) : null;
+  const rules = [xZero ? ruleX([0]) : null, yZero ? ruleY([0]) : null];
+  mark = mark(data, options);
+  return colorMode === "stroke" ? marks(frames, rules, mark) : marks(frames, mark, rules);
+}
+
+function isContinuous(values) {
+  return !isOrdinal(values);
+}
+
+// TODO What about sorted within series?
+function isMonotonic(values) {
+  let previous;
+  let previousOrder;
+  for (const value of values) {
+    if (value == null) continue;
+    if (previous === undefined) {
+      previous = value;
+      continue;
+    }
+    const order = Math.sign(ascending(previous, value));
+    if (!order) continue; // skip zero, NaN
+    if (previousOrder !== undefined && order !== previousOrder) return false;
+    previous = value;
+    previousOrder = order;
+  }
+  return true;
+}
+
+function makeOptions(value) {
+  return isReducer(value) ? {reduce: value} : {value};
+}
+
+// https://github.com/observablehq/plot/blob/818562649280e155136f730fc496e0b3d15ae464/src/transforms/group.js#L236
+function isReducer(reduce) {
+  if (typeof reduce?.reduce === "function") return true;
+  if (/^p\d{2}$/i.test(reduce)) return true;
+  switch (`${reduce}`.toLowerCase()) {
+    case "first":
+    case "last":
+    case "count":
+    case "distinct":
+    case "sum":
+    case "proportion":
+    case "proportion-facet": // TODO remove me?
+    case "deviation":
+    case "min":
+    case "min-index": // TODO remove me?
+    case "max":
+    case "max-index": // TODO remove me?
+    case "mean":
+    case "median":
+    case "variance":
+    case "mode":
+      // These are technically reducers, but I think we’d want to treat them as fields?
+      // case "x":
+      // case "x1":
+      // case "x2":
+      // case "y":
+      // case "y1":
+      // case "y2":
+      return true;
+  }
+  return false;
+}
+
+function isHighCardinality(value) {
+  return value ? new InternSet(value).size > value.length >> 1 : false;
+}