implicit trim for log ticks

src/log.js

@@ -1,5 +1,5 @@
 import {ticks} from "d3-array";
-import {format} from "d3-format";
+import {format, formatSpecifier} from "d3-format";
 import nice from "./nice.js";
 import {copy, transformer} from "./continuous.js";
 import {initRange} from "./init.js";
@@ -111,10 +111,13 @@ export function loggish(transform) {
   };
 
   scale.tickFormat = function(count, specifier) {
+    if (count == null) count = 10;
     if (specifier == null) specifier = base === 10 ? ".0e" : ",";
-    if (typeof specifier !== "function") specifier = format(specifier);
+    if (typeof specifier !== "function") {
+      if (!(base % 1) && (specifier = formatSpecifier(specifier)).precision == null) specifier.trim = true;
+      specifier = format(specifier);
+    }
     if (count === Infinity) return specifier;
-    if (count == null) count = 10;
     var k = Math.max(1, base * count / scale.ticks().length); // TODO fast estimate?
     return function(d) {
       var i = d / pows(Math.round(logs(d)));

test/log-test.js

@@ -401,14 +401,43 @@ it("log.tickFormat(count, format) returns a filtered format", () => {
 
 it("log.tickFormat(count, specifier) returns a filtered format", () => {
   const x = scaleLog().domain([1000.1, 1]);
-  assert.deepStrictEqual(x.ticks().map(x.tickFormat(10, ".1s")), [
+  assert.deepStrictEqual(x.ticks().map(x.tickFormat(10, "s")), [
     "1k",
     "", "", "", "", "", "", "300", "200", "100",
     "", "", "", "", "", "", "30", "20", "10",
     "", "", "", "", "", "", "3", "2", "1"
   ]);
 });
 
+it("log.tickFormat(count, specifier) trims trailing zeroes by default", () => {
+  const x = scaleLog().domain([100.1, 0.02]);
+  assert.deepStrictEqual(x.ticks().map(x.tickFormat(10, "f")), [
+    "100",
+    "", "", "", "", "", "", "", "20", "10",
+    "", "", "", "", "", "", "", "2", "1",
+    "", "", "", "", "", "", "", "0.2", "0.1",
+    "", "", "", "", "", "", "", "0.02"
+  ]);
+});
+
+it("log.tickFormat(count, specifier) with base two trims trailing zeroes by default", () => {
+  const x = scaleLog().base(2).domain([100.1, 0.02]);
+  assert.deepStrictEqual(x.ticks().map(x.tickFormat(10, "f")), [
+    "64", "32", "16", "8", "4", "2", "1", "0.5", "0.25", "0.125", "0.0625", "0.03125"
+  ]);
+});
+
+it("log.tickFormat(count, specifier) preserves trailing zeroes if needed", () => {
+  const x = scaleLog().domain([100.1, 0.02]);
+  assert.deepStrictEqual(x.ticks().map(x.tickFormat(10, ".1f")), [
+    "100.0",
+    "", "", "", "", "", "", "", "20.0", "10.0",
+    "", "", "", "", "", "", "", "2.0", "1.0",
+    "", "", "", "", "", "", "", "0.2", "0.1",
+    "", "", "", "", "", "", "", "0.0"
+  ]);
+});
+
 it("log.ticks() returns the empty array when the domain is degenerate", () => {
   const x = scaleLog();
   assert.deepStrictEqual(x.domain([0, 1]).ticks(), []);