Fix #771 for singleton ordinal domains.

d3.v2.js

@@ -2483,7 +2483,7 @@
     };
     scale.rangePoints = function(x, padding) {
       if (arguments.length < 2) padding = 0;
-      var start = x[0], stop = x[1], step = (stop - start) / (domain.length - 1 + padding);
+      var start = x[0], stop = x[1], step = (stop - start) / (Math.max(1, domain.length - 1) + padding);
       range = steps(domain.length < 2 ? (start + stop) / 2 : start + step * padding / 2, step);
       rangeBand = 0;
       ranger = {

src/scale/ordinal.js

@@ -36,7 +36,7 @@ function d3_scale_ordinal(domain, ranger) {
     if (arguments.length < 2) padding = 0;
     var start = x[0],
         stop = x[1],
-        step = (stop - start) / (domain.length - 1 + padding);
+        step = (stop - start) / (Math.max(1, domain.length - 1) + padding);
     range = steps(domain.length < 2 ? (start + stop) / 2 : start + step * padding / 2, step);
     rangeBand = 0;
     ranger = {t: "rangePoints", a: arguments};

test/scale/ordinal-test.js

@@ -120,6 +120,11 @@ suite.addBatch({
         assert.deepEqual(x.range(), [30, 60, 90]);
         assert.equal(x.rangeBand(), 0);
       },
+      "correctly handles singleton domains": function(ordinal) {
+        var x = ordinal().domain(["a"]).rangePoints([0, 120]);
+        assert.deepEqual(x.range(), [60]);
+        assert.equal(x.rangeBand(), 0);
+      },
       "can be set to a descending range": function(ordinal) {
         var x = ordinal().domain(["a", "b", "c"]).rangePoints([120, 0]);
         assert.deepEqual(x.range(), [120, 60,0]);