Fix tooltip randomly switching when have equal values (#2311)

src/arc.js

@@ -7,7 +7,16 @@ c3_chart_internal_fn.initPie = function () {
     $$.pie = d3.pie().value(function (d) {
         return d.values.reduce(function (a, b) { return a + b.value; }, 0);
     });
-    $$.pie.sort($$.getOrderFunction() || null);
+
+    let orderFct = $$.getOrderFunction();
+
+    // we need to reverse the returned order if asc or desc to have the slice in expected order.
+    if (orderFct && ($$.isOrderAsc() || $$.isOrderDesc())) {
+        let defaultSort = orderFct;
+        orderFct = (t1, t2) => defaultSort(t1, t2) * -1;
+    }
+
+    $$.pie.sort(orderFct || null);
 };
 
 c3_chart_internal_fn.updateRadius = function () {

src/data.js

@@ -190,11 +190,11 @@ c3_chart_internal_fn.isOrderAsc = function () {
 c3_chart_internal_fn.getOrderFunction = function() {
     var $$ = this, config = $$.config, orderAsc = $$.isOrderAsc(), orderDesc = $$.isOrderDesc();
     if (orderAsc || orderDesc) {
-        return function (t1, t2) {
         var reducer = function (p, c) { return p + Math.abs(c.value); };
+        return function (t1, t2) {
             var t1Sum = t1.values.reduce(reducer, 0),
                 t2Sum = t2.values.reduce(reducer, 0);
-            return orderDesc ? t2Sum - t1Sum : t1Sum - t2Sum;
+            return orderAsc ? t2Sum - t1Sum : t1Sum - t2Sum;
         };
     } else if (isFunction(config.data_order)) {
         return config.data_order;
@@ -209,9 +209,6 @@ c3_chart_internal_fn.orderTargets = function (targets) {
     var fct = this.getOrderFunction();
     if (fct) {
         targets.sort(fct);
-        if (this.isOrderAsc() || this.isOrderDesc()) {
-            targets.reverse();
-        }
     }
     return targets;
 };