fix crash on missing top bin (#248)

* fix https://observablehq.com/@weiglemc/demonstrating-issue-with-d3-bins-in-d3v7-4-1-update

the issue is that we have removed the last bin, but then want to assign the largest value to it because floor(x1) === x1

Co-authored-by: Mike Bostock <mbostock@gmail.com>

src/bin.js

@@ -85,14 +85,14 @@ export default function bin() {
       if (step > 0) {
         for (i = 0; i < n; ++i) {
           if ((x = values[i]) != null && x0 <= x && x <= x1) {
-            bins[Math.floor((x - x0) / step)].push(data[i]);
+            bins[Math.min(m, Math.floor((x - x0) / step))].push(data[i]);
           }
         }
       } else if (step < 0) {
         for (i = 0; i < n; ++i) {
           if ((x = values[i]) != null && x0 <= x && x <= x1) {
             const j = Math.floor((x0 - x) * step);
-            bins[j + (tz[j] <= x)].push(data[i]); // handle off-by-one due to rounding
+            bins[Math.min(m, j + (tz[j] <= x))].push(data[i]); // handle off-by-one due to rounding
           }
         }
       }

test/bin-test.js

@@ -235,6 +235,12 @@ it("bin(data) assigns floating point values to the correct bins", () => {
   }
 });
 
+it("bin(data) assigns integer values to the correct bins", () => {
+  assert.deepStrictEqual(bin().domain([4, 5])([5]), [box([5], 4, 5)]);
+  const eights = [8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8];
+  assert.deepStrictEqual(bin().domain([3, 8])(eights), [box([], 3, 4), box([], 4, 5), box([], 5, 6), box([], 6, 7), box(eights, 7, 8)]);
+});
+
 function box(bin, x0, x1)  {
   bin.x0 = x0;
   bin.x1 = x1;