Error on bad min_cluster_size as per #48

Author: lmcinnes

hdbscan/hdbscan_.py

@@ -454,6 +454,9 @@ def hdbscan(X, min_cluster_size=5, min_samples=None, alpha=1.0,
         raise ValueError('Min samples and Min cluster size must be positive'
                          ' integers')
 
+    if min_cluster_size == 1:
+        raise ValueError('Min cluster size must be greater than one')
+
     if not isinstance(alpha, float) or alpha <= 0.0:
         raise ValueError('Alpha must be a positive float value greater than'
                          ' 0!')