TPointArray.Median: [1,3,5] returned 4 not 3 and [1,3,5,7] returned 5 not 4.

TPointArray.Mean: Use Int64 for Mean sums

+ added test

Author: ollydev

Source/simba.res

@@ -987,21 +987,26 @@ function TPointArrayHelper.Mean: TPoint;
 var
   Ptr: PPoint;
   Upper: PtrUInt;
+  SumX, SumY: Int64;
 begin
   Result := TPoint.ZERO;
   if (Length(Self) = 0) then
     Exit;
 
+  SumX := 0;
+  SumY := 0;
+
   Ptr := @Self[0];
   Upper := PtrUInt(Ptr) + (Length(Self) * SizeOf(TPoint));
   while (PtrUInt(Ptr) < Upper) do
   begin
-    Inc(Result.X, Ptr^.X);
-    Inc(Result.Y, Ptr^.Y);
+    Inc(SumX, Ptr^.X);
+    Inc(SumY, Ptr^.Y);
     Inc(Ptr);
   end;
 
-  Result := Result div Length(Self);
+  Result.X := SumX div Length(Self);
+  Result.Y := SumY div Length(Self);
 end;
 
 function TPointArrayHelper.MinAreaRect: TQuad;
@@ -2783,14 +2788,14 @@ function TPointArrayHelper.Median: TPoint;
 
     Mid := Length(Self) div 2;
 
-    if (Length(Self) mod 2) = 0 then
+    if (Length(Self) mod 2) = 1 then
     begin
       Result.X := X[Mid];
       Result.Y := Y[Mid];
     end else
     begin
-      Result.X := Round((X[Mid] + X[Mid+1]) / 2);
-      Result.Y := Round((Y[Mid] + Y[Mid+1]) / 2);
+      Result.X := Round((X[Mid-1] + X[Mid]) / 2);
+      Result.Y := Round((Y[Mid-1] + Y[Mid]) / 2);
     end;
   end;
 end;

Source/simba.vartype_pointarray.pas

@@ -0,0 +1,41 @@
+{$assertions on}
+
+procedure TestMean;
+var
+  arr: TPointArray;
+  i: Int32;
+begin
+  Assert(TPointArray([]).Mean() = Point(0, 0), 'Mean of empty');
+  Assert(TPointArray([Point(1, 1), Point(2, 2)]).Mean() = Point(1, 1), 'Mean truncates');
+
+  arr := TPointArray.CreateFromBox(TBox.Create(0, 0, 10, 10), True);
+  Assert(arr.Mean() = Point(5, 5), 'Mean of symmetric box');
+  arr += Point(1000, 1000);
+  Assert(arr.Mean() = Point(13, 13), 'Mean should be dragged by outlier');
+
+  // check overflowing
+  SetLength(arr, 2000);
+  for i := 0 to High(arr) do
+    arr[i] := Point(2000000, 2000000);
+  Assert(arr.Mean() = Point(2000000, 2000000), 'Mean overflowed on a large sum');
+end;
+
+procedure TestMedian;
+var
+  arr: TPointArray;
+begin
+  Assert(TPointArray([]).Median() = Point(0, 0), 'Median of empty');
+  Assert(TPointArray([Point(9, 9), Point(1, 1), Point(5, 5)]).Median() = Point(5, 5), 'Median odd');
+  Assert(TPointArray([Point(1, 1), Point(3, 3), Point(5, 5), Point(7, 7)]).Median() = Point(4, 4), 'Median even');
+  Assert(TPointArray([Point(0, 10), Point(5, 0), Point(10, 5)]).Median() = Point(5, 5), 'Median is per axis');
+
+  arr := TPointArray.CreateFromBox(TBox.Create(0, 0, 10, 10), True);
+  Assert(arr.Median() = Point(5, 5), 'Median of symmetric box');
+  arr += Point(1000, 1000);
+  Assert(arr.Median() = Point(5, 5), 'Median outlier should be unaffected');
+end;
+
+begin
+  TestMean();
+  TestMedian();
+end.