text identity

README.md

@@ -1089,7 +1089,7 @@ The following channels are required:
 
 * **text** - the text contents (a string, possibly with multiple lines)
 
-If the **text** contains `\n`, `\r\n`, or `\r`, it will be rendered as multiple lines via tspan elements. If the **text** is specified as numbers or dates, a default formatter will automatically be applied, and the **fontVariant** will default to tabular-nums instead of normal. For more control over number and date formatting, consider [*number*.toLocaleString](https://observablehq.com/@mbostock/number-formatting), [*date*.toLocaleString](https://observablehq.com/@mbostock/date-formatting), [d3-format](https://github.com/d3/d3-format), or [d3-time-format](https://github.com/d3/d3-time-format). If **text** is not specified, it defaults to [0, 1, 2, …] so that something is visible by default.
+If the **text** contains `\n`, `\r\n`, or `\r`, it will be rendered as multiple lines via tspan elements. If the **text** is specified as numbers or dates, a default formatter will automatically be applied, and the **fontVariant** will default to tabular-nums instead of normal. For more control over number and date formatting, consider [*number*.toLocaleString](https://observablehq.com/@mbostock/number-formatting), [*date*.toLocaleString](https://observablehq.com/@mbostock/date-formatting), [d3-format](https://github.com/d3/d3-format), or [d3-time-format](https://github.com/d3/d3-time-format). If **text** is not specified, it defaults to the identity function for primitive data (such as numbers, dates, and strings), and to the zero-based index [0, 1, 2, …] for objects (so that something identifying is visible by default).
 
 In addition to the [standard mark options](#marks), the following optional channels are supported:
 

src/marks/text.js

@@ -1,7 +1,7 @@
 import {create, isoFormat, namespaces} from "d3";
 import {nonempty} from "../defined.js";
 import {formatNumber} from "../format.js";
-import {indexOf, identity, string, maybeNumberChannel, maybeTuple, numberChannel, isNumeric, isTemporal, keyword, maybeFrameAnchor} from "../options.js";
+import {indexOf, identity, string, maybeNumberChannel, maybeTuple, numberChannel, isNumeric, isTemporal, keyword, maybeFrameAnchor, isTextual} from "../options.js";
 import {Mark} from "../plot.js";
 import {applyChannelStyles, applyDirectStyles, applyIndirectStyles, applyAttr, applyTransform, offset, impliedString, applyFrameAnchor} from "../style.js";
 
@@ -14,7 +14,7 @@ export class Text extends Mark {
     const {
       x,
       y,
-      text = indexOf,
+      text = data != null && isTextual(data) ? identity : indexOf,
       textAnchor,
       lineAnchor = "middle",
       lineHeight = 1,

src/options.js

@@ -187,6 +187,13 @@ export function numberChannel(source) {
   };
 }
 
+export function isTextual(values) {
+  for (const value of values) {
+    if (value == null) continue;
+    return typeof value !== "object" || value instanceof Date;
+  }
+}
+
 export function isOrdinal(values) {
   for (const value of values) {
     if (value == null) continue;

test/marks/text-test.js

@@ -21,11 +21,36 @@ it("text() has the expected defaults", () => {
   assert.strictEqual(text.shapeRendering, undefined);
   assert.strictEqual(text.textAnchor, undefined);
   assert.strictEqual(text.lineAnchor, "middle");
+  assert.strictEqual(text.frameAnchor, "middle");
   assert.strictEqual(text.dx, 0);
   assert.strictEqual(text.dy, 0);
   assert.strictEqual(text.rotate, 0);
 });
 
+it("text(strings, {frameAnchor}) has the expected defaults", () => {
+  const data = ["hello"];
+  const text = Plot.text(data, {frameAnchor: "middle"});
+  assert.strictEqual(text.data, data);
+  assert.strictEqual(text.transform, undefined);
+  assert.deepStrictEqual(text.channels.map(c => c.name), ["text"]);
+  assert.deepStrictEqual(text.channels.map(c => Plot.valueof(data, c.value)), [data]);
+  assert.strictEqual(text.textAnchor, undefined);
+  assert.strictEqual(text.lineAnchor, "middle");
+  assert.strictEqual(text.frameAnchor, "middle");
+});
+
+it("text(dates, {frameAnchor}) has the expected defaults", () => {
+  const data = [new Date("2021-01-01")];
+  const text = Plot.text(data, {frameAnchor: "middle"});
+  assert.strictEqual(text.data, data);
+  assert.strictEqual(text.transform, undefined);
+  assert.deepStrictEqual(text.channels.map(c => c.name), ["text"]);
+  assert.deepStrictEqual(text.channels.map(c => Plot.valueof(data, c.value)), [data]);
+  assert.strictEqual(text.textAnchor, undefined);
+  assert.strictEqual(text.lineAnchor, "middle");
+  assert.strictEqual(text.frameAnchor, "middle");
+});
+
 it("text(data, {title}) specifies an optional title channel", () => {
   const text = Plot.text(undefined, {title: "x"});
   const title = text.channels.find(c => c.name === "title");