Merge pull request #65 from tommilligan/kneelocator-index-error

knee_locator: don't raise IndexError if no knee is found

kneed/knee_locator.py

@@ -93,8 +93,12 @@ def __init__(
 
         # Step 6: find knee
         self.knee, self.norm_knee = self.find_knee()
-        self.knee_y = self.y[self.x == self.knee][0]
-        self.norm_knee_y = self.y_normalized[self.x_normalized == self.norm_knee][0]
+
+        # Step 7: If we have a knee, extract data about it
+        self.knee_y = self.norm_knee_y = None
+        if self.knee:
+            self.knee_y = self.y[self.x == self.knee][0]
+            self.norm_knee_y = self.y_normalized[self.x_normalized == self.norm_knee][0]
 
     @staticmethod
     def __normalize(a: Iterable[float]) -> Iterable[float]:

tests/test_sample.py

@@ -177,3 +177,17 @@ def test_y():
     assert math.isclose(kl.all_knees_y[0], 1.897, rel_tol=0.03)
     assert math.isclose(kl.norm_knee_y, 0.758, rel_tol=0.03)
     assert math.isclose(kl.all_norm_knees_y[0], 0.758, rel_tol=0.03)
+
+def test_y_no_knee():
+    """Test the y value, if there is no knee found."""
+    kl = KneeLocator(
+        np.array([1, 2, 3]),
+        np.array([0.90483742, 0.81873075, 0.74081822]),
+        S=1.0,
+        curve="convex",
+        direction="decreasing",
+        interp_method="interp1d",
+        online=False
+    )
+    assert kl.knee_y is None
+    assert kl.norm_knee_y is None