handle misaligned intervals

src/marks/axis.js

@@ -547,6 +547,7 @@ function axisMark(mark, k, ariaLabel, data, options, initialize) {
           const [start, stop] = extent(data);
           if (interval) {
             data = maybeRangeInterval(interval, type).range(start, stop);
+            data = data.map(scale.interval.floor, scale.interval);
           } else {
             if (ticks === undefined) {
               const [min, max] = extent(scale.range());

src/time.js

@@ -145,11 +145,12 @@ export function formatTimeTicks(scale, data = scale.domain(), ticks, anchor) {
 // the ticks show the field that is changing. If the ticks are not available,
 // fallback to an approximation based on the desired number of ticks.
 function getTimeTicksInterval(scale, data, ticks) {
-  const medianStep = median(pairs(data, (a, b) => Math.abs(b - a) || NaN));
-  if (medianStep > 0) return formats[bisector(([, step]) => step).right(formats, medianStep, 1, formats.length) - 1][0];
-  const [start, stop] = extent(scale.domain());
-  const count = typeof ticks === "number" ? ticks : 10;
-  const step = Math.abs(stop - start) / count;
+  let step = median(pairs(data, (a, b) => Math.abs(b - a) || NaN));
+  if (!(step > 0)) {
+    const [start, stop] = extent(scale.domain());
+    const count = typeof ticks === "number" ? ticks : 10;
+    step = Math.abs(stop - start) / count;
+  }
   return formats[bisector(([, step]) => Math.log(step)).center(formats, Math.log(step))][0];
 }
 

test/plots/time-axis.ts

@@ -91,6 +91,14 @@ export async function timeAxisOrdinal() {
   });
 }
 
+export async function timeAxisOrdinalIrregular() {
+  const aapl = await d3.csv<any>("data/aapl.csv", d3.autoType);
+  return Plot.plot({
+    x: {interval: "4 weeks", ticks: "year"},
+    marks: [Plot.barY(aapl, Plot.groupX({y: "median", title: "min"}, {title: "Date", x: "Date", y: "Close"}))]
+  });
+}
+
 export async function timeAxisOrdinalTicks() {
   const aapl = await d3.csv<any>("data/aapl.csv", d3.autoType);
   return Plot.plot({