Fixes incorrect output for precomputed input

Akshay0724 · Akshay0724 · commit 7e044d4d798a · 2017-02-11T22:42:07.000+05:30
diff --git a/sklearn/cluster/dbscan_.py b/sklearn/cluster/dbscan_.py
@@ -121,6 +121,17 @@ def dbscan(X, eps=0.5, min_samples=5, metric='minkowski', metric_params=None,
     # neighborhood of point i. While True, its useless information)
     if metric == 'precomputed' and sparse.issparse(X):
         neighborhoods = np.empty(X.shape[0], dtype=object)
+        
+        #Modify X so that every element first row are not zero
+        if X.indptr[0] == X.indptr[1] == 0:
+            indptr = X.indptr
+            indptr = indptr+1
+            indptr[1] = 1
+            indptr[0] = 0
+            indices = np.insert(X.indices, 0, 0)
+            data = np.insert(X.data, 0, eps+1)
+            X = sparse.csr_matrix((data, indices, indptr), shape=X.shape)
+
         X.sum_duplicates()  # XXX: modifies X's internals in-place
         X_mask = X.data <= eps
         masked_indices = astype(X.indices, np.intp, copy=False)[X_mask]
