sort aliases

README.md

@@ -420,7 +420,7 @@ If an ordinal scale’s domain is not set, it defaults to natural ascending orde
 Plot.barY(alphabet, {x: "letter", y: "frequency", sort: {x: "y"}})
 ```
 
-The sort option is an object whose keys are ordinal scale names, such as *x* or *fx*, and whose values are mark channel names, such as *y*, *y1*, or *y2*. By specifying an existing channel rather than a new value, you avoid repeating the order definition and can refer to channels derived by [transforms](#transforms) (such as [stack](#stack) or [bin](#bin)). For marks that implicitly stack ([area](#area), [bar](#bar), and [rect](#rect)), the stacked dimension is aliased: when stacking on *x*, *x* is an alias for *x2*, and when stacking on *y*, *y* is an alias for *y2*.
+The sort option is an object whose keys are ordinal scale names, such as *x* or *fx*, and whose values are mark channel names, such as *y*, *y1*, or *y2*. By specifying an existing channel rather than a new value, you avoid repeating the order definition and can refer to channels derived by [transforms](#transforms) (such as [stack](#stack) or [bin](#bin)). When sorting on the *x*, if no such channel is defined, the *x2* channel will be used instead if available, and similarly for *y* and *y2*; this is useful for marks that implicitly stack such as [area](#area), [bar](#bar), and [rect](#rect). A sort value may also be specified as *width* or *height*, representing derived channels |*x2* - *x1*| and |*y2* - *y1*| respectively.
 
 Note that there may be multiple associated values in the secondary dimension for a given value in the primary ordinal dimension. The secondary values are therefore grouped for each associated primary value, and each group is then aggregated by applying a reducer. Lastly the primary values are sorted based on the associated reduced value in natural ascending order to produce the domain. The default reducer is *max*, but may be changed by specifying the *reduce* option. The above code is shorthand for:
 

src/channel.js

@@ -19,7 +19,8 @@ export function channelSort(channels, facetChannels, data, options) {
   const {reverse: defaultReverse, reduce: defaultReduce = true, limit: defaultLimit} = options;
   for (const x in options) {
     if (!registry.has(x)) continue; // ignore unknown scale keys
-    const {value: y, reverse = defaultReverse, reduce = defaultReduce, limit = defaultLimit} = maybeValue(options[x]);
+    let {value: y, reverse = defaultReverse, reduce = defaultReduce, limit = defaultLimit} = maybeValue(options[x]);
+    if (reverse === undefined) reverse = y === "width" || y === "height"; // default to descending for lengths
     if (reduce == null || reduce === false) continue; // disabled reducer
     const X = channels.find(([, {scale}]) => scale === x) || facetChannels && facetChannels.find(([, {scale}]) => scale === x);
     if (!X) throw new Error(`missing channel for scale: ${x}`);
@@ -33,14 +34,10 @@ export function channelSort(channels, facetChannels, data, options) {
         return domain;
       };
     } else {
-      let YV;
-      if (y === "data") {
-        YV = data;
-      } else {
-        const Y = channels.find(([name]) => name === y);
-        if (!Y) throw new Error(`missing channel: ${y}`);
-        YV = Y[1].value;
-      }
+      const YV = y === "data" ? data
+          : y === "height" ? difference(channels, "y1", "y2")
+          : y === "width" ? difference(channels, "x1", "x2")
+          : values(channels, y, y === "y" ? "y2" : y === "x" ? "x2" : undefined);
       const reducer = maybeReduce(reduce === true ? "max" : reduce, YV);
       X[1].domain = () => {
         let domain = rollup(range(XV), I => reducer.reduce(I, YV), i => XV[i]);
@@ -52,6 +49,19 @@ export function channelSort(channels, facetChannels, data, options) {
   }
 }
 
+function difference(channels, k1, k2) {
+  const X1 = values(channels, k1);
+  const X2 = values(channels, k2);
+  return Float64Array.from(X2, (x2, i) => Math.abs(x2 - X1[i]));
+}
+
+function values(channels, name, alias) {
+  let channel = channels.find(([n]) => n === name);
+  if (!channel && alias !== undefined) channel = channels.find(([n]) => n === alias);
+  if (channel) return channel[1].value;
+  throw new Error(`missing channel: ${name}`);
+}
+
 function ascendingGroup([ak, av], [bk, bv]) {
   return ascending(av, bv) || ascending(ak, bk);
 }

src/transforms/stack.js

@@ -1,6 +1,6 @@
 import {InternMap, cumsum, group, groupSort, greatest, max, min, rollup, sum} from "d3";
 import {ascendingDefined} from "../defined.js";
-import {field, lazyChannel, maybeLazyChannel, maybeZ, mid, range, valueof, maybeZero, isOptions, maybeValue} from "../options.js";
+import {field, lazyChannel, maybeLazyChannel, maybeZ, mid, range, valueof, maybeZero} from "../options.js";
 import {basic} from "./basic.js";
 
 export function stackX(stackOptions = {}, options = {}) {
@@ -46,29 +46,17 @@ export function stackY2(stackOptions = {}, options = {}) {
 }
 
 export function maybeStackX({x, x1, x2, ...options} = {}) {
-  options = aliasSort(options, "x");
   if (x1 === undefined && x2 === undefined) return stackX({x, ...options});
   ([x1, x2] = maybeZero(x, x1, x2));
   return {...options, x1, x2};
 }
 
 export function maybeStackY({y, y1, y2, ...options} = {}) {
-  options = aliasSort(options, "y");
   if (y1 === undefined && y2 === undefined) return stackY({y, ...options});
   ([y1, y2] = maybeZero(y, y1, y2));
   return {...options, y1, y2};
 }
 
-function aliasSort(options, name) {
-  let {sort} = options;
-  if (!isOptions(sort)) return options;
-  for (const x in sort) {
-    const {value: y, ...rest} = maybeValue(sort[x]);
-    if (y === name) sort = {...sort, [x]: {value: `${y}2`, ...rest}};
-  }
-  return {...options, sort};
-}
-
 // The reverse option is ambiguous: it is both a stack option and a basic
 // transform. If only one options object is specified, we interpret it as a
 // stack option, and therefore must remove it from the propagated options.

test/data/README.md

@@ -43,6 +43,10 @@ https://github.com/hemanrobinson/preattentive/blob/a58dd4795d0ee063a38a2d7bf3381
 ggplot2 “diamonds” dataset (carat and price columns only)
 https://github.com/tidyverse/ggplot2/blob/master/data-raw/diamonds.csv
 
+## energy-production.csv
+U.S. Energy Information Administration; monthly energy review, primary energy production by source, Jan. 2022
+https://www.eia.gov/totalenergy/data/monthly/index.php
+
 ## gistemp.csv
 NASA Goddard Institute for Space Studies
 https://data.giss.nasa.gov/gistemp/