Fixes sum when the min value and the first bin's mean are the same

Author: ashenfad

src/java/com/bigml/histogram/Histogram.java

@@ -339,10 +339,12 @@ public SumResult<T> extendedSum(double p) throws SumOutOfRangeException {
         bin_i1 = new Bin(_maximum, 0, emptyTarget.clone());
       }
 
-      double prevCount = 0;
-      T prevTargetSum = (T) emptyTarget.clone();
-
-      if (bin_i.getMean() != _minimum) {
+      double prevCount;
+      T prevTargetSum;
+      if (bin_i.getMean() == _minimum) {
+        prevCount = _bins.first().getCount() / 2;
+        prevTargetSum = (T) _bins.first().getTarget().clone().mult(0.5);
+      } else {
         SumResult<T> prevSumResult = getPointToSumMap().get(bin_i.getMean());
         prevCount = prevSumResult.getCount();
         prevTargetSum = prevSumResult.getTargetSum();

test/bigml/histogram/test/core.clj

@@ -342,3 +342,9 @@
 
 (deftest nil-target-sum
   (is (nil? (total-target-sum (create)))))
+
+(deftest sum-edges
+  (let [hist (reduce insert! (create) [0 10])]
+    (is (== 1 (sum hist 5)))
+    (is (== 0.5 (sum hist 0)))
+    (is (== 2 (sum hist 10)))))