Rewrite stackOrderAppearance.

README.md

@@ -1101,6 +1101,10 @@ function offsetNone(series, order) {
 
 Stack orders are typically not used directly, but are instead passed to [*stack*.order](#stack_order).
 
+<a name="stackOrderAppearance" href="#stackOrderAppearance">#</a> d3.<b>stackOrderAppearance</b>(<i>series</i>) [<>](https://github.com/d3/d3-shape/blob/master/src/order/appearance.js "Source")
+
+Returns a series order such that the earliest series (according to the first non-zero value) is at the bottom.
+
 <a name="stackOrderAscending" href="#stackOrderAscending">#</a> d3.<b>stackOrderAscending</b>(<i>series</i>) [<>](https://github.com/d3/d3-shape/blob/master/src/order/ascending.js "Source")
 
 Returns a series order such that the smallest series (according to the sum of values) is at the bottom.

src/index.js

@@ -38,6 +38,7 @@ export {default as stackOffsetDiverging} from "./offset/diverging";
 export {default as stackOffsetNone} from "./offset/none";
 export {default as stackOffsetSilhouette} from "./offset/silhouette";
 export {default as stackOffsetWiggle} from "./offset/wiggle";
+export {default as stackOrderAppearance} from "./order/appearance";
 export {default as stackOrderAscending} from "./order/ascending";
 export {default as stackOrderDescending} from "./order/descending";
 export {default as stackOrderInsideOut} from "./order/insideOut";

src/order/appearance.js

@@ -1,10 +1,12 @@
+import none from "./none";
+
 export default function(series) {
-  var appearanceIndex = series.map(function(d,i){
-    for(var k = 0, n = d.length;k < n;++k){
-      if(d[k][1] > 0) break;
-    }
-    return [k, i];
-  });
-  appearanceIndex.sort(function(a,b){return a[0] - b[0];})
-  return appearanceIndex.map(function(d){return d[1]});
+  var starts = series.map(start);
+  return none(series).sort(function(a, b) { return starts[a] - starts[b]; });
+}
+
+function start(series) {
+  var i = -1, n = series.length;
+  while (++i < n && !+series[i][1]);
+  return i;
 }

test/order/appearance-test.js

@@ -0,0 +1,20 @@
+var tape = require("tape"),
+    shape = require("../../");
+
+tape("stackOrderAppearance(series) returns an order by appearance", function(test) {
+  test.deepEqual(shape.stackOrderAppearance([
+    [[0, 0], [0, 0], [0, 0]],
+    [[0, 0], [0, 2], [0, 3]],
+    [[0, 0], [0, 0], [0, 4]]
+  ]), [1, 2, 0]);
+  test.end();
+});
+
+tape("stackOrderAppearance(series) treats NaN values as zero", function(test) {
+  test.deepEqual(shape.stackOrderAppearance([
+    [[0, 0], [0, NaN], [0, NaN]],
+    [[0, 0], [0, 2], [0, 3]],
+    [[0, 0], [0, NaN], [0, 4]]
+  ]), [1, 2, 0]);
+  test.end();
+});