addEntryOrdered to automatically place the entry in the correct index (…

…#173)

addEntry is unordered, and currently assumes that it is the last entry.
In the future when we will have charts with optionally unordered data, addEntry will be useful, while not addEntryOrdered is useful when adding entries in the middle of the dataset.

Charts/Classes/Data/ChartDataSet.swift

@@ -280,6 +280,8 @@ public class ChartDataSet: NSObject
     /// Returns the number of entries this DataSet holds.
     public var valueCount: Int { return _yVals.count; }
 
+    /// Adds an entry to the end of the yVals array
+    /// :param: e the entry to add
     public func addEntry(e: ChartDataEntry)
     {
         var val = e.value
@@ -311,6 +313,50 @@ public class ChartDataSet: NSObject
         _yVals.append(e)
     }
 
+    /// Adds an entry, and inserting it at the appropriate index in the yVals array, according to it's x-index.
+    /// :param: e the entry to add
+    public func addEntryOrdered(e: ChartDataEntry)
+    {
+        var val = e.value
+
+        if (_yVals == nil)
+        {
+            _yVals = [ChartDataEntry]()
+        }
+
+        if (_yVals.count == 0)
+        {
+            _yMax = val
+            _yMin = val
+        }
+        else
+        {
+            if (_yMax < val)
+            {
+                _yMax = val
+            }
+            if (_yMin > val)
+            {
+                _yMin = val
+            }
+        }
+
+        _yValueSum += val
+
+        if _yVals.last?.xIndex > e.xIndex
+        {
+            var closestIndex = entryIndex(xIndex: e.xIndex)
+            if _yVals[closestIndex].xIndex < e.xIndex
+            {
+                closestIndex++
+            }
+            _yVals.insert(e, atIndex: closestIndex)
+            return;
+        }
+
+        _yVals.append(e)
+    }
+
     public func removeEntry(entry: ChartDataEntry) -> Bool
     {
         var removed = false