Put zero values at zero.

README.md

@@ -1134,7 +1134,7 @@ Applies a zero baseline and normalizes the values for each point such that the t
 
 <a name="stackOffsetDiverging" href="#stackOffsetDiverging">#</a> d3.<b>stackOffsetDiverging</b>(<i>series</i>, <i>order</i>) · [Source](https://github.com/d3/d3-shape/blob/master/src/offset/diverging.js)
 
-Positive values are stacked above zero, while negative values are [stacked below zero](https://bl.ocks.org/mbostock/b5935342c6d21928111928401e2c8608).
+Positive values are stacked above zero, negative values are [stacked below zero](https://bl.ocks.org/mbostock/b5935342c6d21928111928401e2c8608), and zero values are stacked at zero.
 
 <a name="stackOffsetNone" href="#stackOffsetNone">#</a> d3.<b>stackOffsetNone</b>(<i>series</i>, <i>order</i>) · [Source](https://github.com/d3/d3-shape/blob/master/src/offset/none.js)
 

src/offset/diverging.js

@@ -2,12 +2,12 @@ export default function(series, order) {
   if (!((n = series.length) > 0)) return;
   for (var i, j = 0, d, dy, yp, yn, n, m = series[order[0]].length; j < m; ++j) {
     for (yp = yn = 0, i = 0; i < n; ++i) {
-      if ((dy = (d = series[order[i]][j])[1] - d[0]) >= 0) {
+      if ((dy = (d = series[order[i]][j])[1] - d[0]) > 0) {
         d[0] = yp, d[1] = yp += dy;
       } else if (dy < 0) {
         d[1] = yn, d[0] = yn += dy;
       } else {
-        d[0] = yp;
+        d[0] = 0, d[1] = dy;
       }
     }
   }

test/offset/diverging-test.js

@@ -16,7 +16,7 @@ tape("stackOffsetDiverging(series, order) applies a zero baseline, ignoring exis
   test.end();
 });
 
-tape.only("stackOffsetDiverging(series, order) handles a single series", function(test) {
+tape("stackOffsetDiverging(series, order) handles a single series", function(test) {
   var series = [
     [[1, 2], [2, 4], [3, 4]]
   ];
@@ -38,7 +38,7 @@ tape("stackOffsetDiverging(series, order) treats NaN as zero", function(test) {
   series[1][1][1] = "NaN"; // can’t test.equal NaN
   test.deepEqual(series, [
     [[0, 1], [0,     2], [0, 1]],
-    [[1, 4], [2, "NaN"], [1, 3]],
+    [[1, 4], [0, "NaN"], [1, 3]],
     [[4, 9], [2,     4], [3, 7]]
   ]);
   test.end();
@@ -73,3 +73,18 @@ tape("stackOffsetDiverging(series, order) puts negative values below zero, in or
   ]);
   test.end();
 });
+
+tape("stackOffsetDiverging(series, order) puts zero values at zero, in order", function(test) {
+  var series = [
+    [[0, 1], [0, 2], [0, -1]],
+    [[0, 3], [0, 0], [0, 0]],
+    [[0, 5], [0, 2], [0, 4]]
+  ];
+  shape.stackOffsetDiverging(series, shape.stackOrderNone(series));
+  test.deepEqual(series, [
+    [[0, 1], [0, 2], [-1, 0]],
+    [[1, 4], [0, 0], [0, 0]],
+    [[4, 9], [2, 4], [0, 4]]
+  ]);
+  test.end();
+});