Fix bug in Utils.binarySearchLessThan

src/main/java/ca/joeltherrien/randomforest/utils/Utils.java

@@ -79,6 +79,10 @@ public final class Utils {
             return endIndex - 1;
         }
 
+        if(x[startIndex] > time){
+            return -1;
+        }
+
         if(range < 200){
             for(int i = startIndex; i < endIndex; i++){
                 if(x[i] > time){
@@ -90,7 +94,7 @@ public final class Utils {
         // else
 
 
-        final int middle = range / 2;
+        final int middle = startIndex + range / 2;
         final double middleTime = x[middle];
         if(middleTime < time){
             // go right

src/test/java/ca/joeltherrien/randomforest/TestUtils.java

@@ -7,6 +7,8 @@ import org.junit.jupiter.api.Test;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
+import java.util.function.DoubleSupplier;
+import java.util.stream.DoubleStream;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -115,4 +117,40 @@ public class TestUtils {
         }
     }
 
+    @Test
+    public void testBinarySearchLessThan(){
+        /*
+        There was a bug where I didn't add startIndex to range/2 for middle; no other tests caught it!
+         */
+        final int n = 10000;
+
+        double[] x = DoubleStream.generate(new DoubleSequenceGenerator()).limit(n).toArray();
+
+
+        for(int i = 0; i < n; i=i+100){
+            final int index = Utils.binarySearchLessThan(0, n, x, i);
+            final int indexOff = Utils.binarySearchLessThan(0, n, x, ((double) i) + 1.5);
+
+            assertEquals(i, index);
+            assertEquals(i+1, indexOff);
+        }
+
+        final int indexTooFar = Utils.binarySearchLessThan(0, n, x, n + 100);
+        assertEquals(n-1, indexTooFar);
+
+        final int indexTooEarly = Utils.binarySearchLessThan(0, n, x, -100);
+        assertEquals(-1, indexTooEarly);
+
+
+    }
+
+    private static class DoubleSequenceGenerator implements DoubleSupplier {
+        private double previous = 0.0;
+
+        @Override
+        public double getAsDouble() {
+            return previous++;
+        }
+    }
+
 }