Implement lazy totals calculation in the DataView.

Add a ‘lazyTotalsCalculation’ grouping info option (default = false)
that delays the totals calculation until the item is accessed via
getItem(index).  This can dramatically improve the perceived
performance of the DataView operations on very large datasets.

1 files changed, 15 insertions, 8 deletions

diff --git a/examples/example-grouping.html b/examples/example-grouping.html
index 86bbd4a..356ade7 100644
--- a/examples/example-grouping.html
+++ b/examples/example-grouping.html
@@ -170,7 +170,8 @@ function groupByDuration() {
       new Slick.Data.Aggregators.Avg("percentComplete"),
       new Slick.Data.Aggregators.Sum("cost")
     ],
-    aggregateCollapsed: false
+    aggregateCollapsed: false,
+    lazyTotalsCalculation: true
   });
 }
 
@@ -187,7 +188,8 @@ function groupByDurationOrderByCount(aggregateCollapsed) {
       new Slick.Data.Aggregators.Avg("percentComplete"),
       new Slick.Data.Aggregators.Sum("cost")
     ],
-    aggregateCollapsed: aggregateCollapsed
+    aggregateCollapsed: aggregateCollapsed,
+    lazyTotalsCalculation: true
   });
 }
 
@@ -202,7 +204,8 @@ function groupByDurationEffortDriven() {
         new Slick.Data.Aggregators.Sum("duration"),
         new Slick.Data.Aggregators.Sum("cost")
       ],
-      aggregateCollapsed: true
+      aggregateCollapsed: true,
+      lazyTotalsCalculation: true
     },
     {
       getter: "effortDriven",
@@ -213,7 +216,8 @@ function groupByDurationEffortDriven() {
         new Slick.Data.Aggregators.Avg("percentComplete"),
         new Slick.Data.Aggregators.Sum("cost")
       ],
-      collapsed: true
+      collapsed: true,
+      lazyTotalsCalculation: true
     }
   ]);
 }
@@ -229,7 +233,8 @@ function groupByDurationEffortDrivenPercent() {
         new Slick.Data.Aggregators.Sum("duration"),
         new Slick.Data.Aggregators.Sum("cost")
       ],
-      aggregateCollapsed: true
+      aggregateCollapsed: true,
+      lazyTotalsCalculation: true
     },
     {
       getter: "effortDriven",
@@ -239,7 +244,8 @@ function groupByDurationEffortDrivenPercent() {
       aggregators :[
         new Slick.Data.Aggregators.Sum("duration"),
         new Slick.Data.Aggregators.Sum("cost")
-      ]
+      ],
+      lazyTotalsCalculation: true
     },
     {
       getter: "percentComplete",
@@ -250,7 +256,8 @@ function groupByDurationEffortDrivenPercent() {
         new Slick.Data.Aggregators.Avg("percentComplete")
       ],
       aggregateCollapsed: true,
-      collapsed: true
+      collapsed: true,
+      lazyTotalsCalculation: true
     }
   ]);
 }
@@ -265,7 +272,7 @@ function loadData(count) {
     d["id"] = "id_" + i;
     d["num"] = i;
     d["title"] = "Task " + i;
-    d["duration"] = Math.round(Math.random() * 14);
+    d["duration"] = Math.round(Math.random() * 30);
     d["percentComplete"] = Math.round(Math.random() * 100);
     d["start"] = someDates[ Math.floor((Math.random()*2)) ];
     d["finish"] = someDates[ Math.floor((Math.random()*2)) ];