Merge branch 'GH2803'

* GH2803:
  BUG: SparseSeries.density shouldn't die GH2803
  TST: SparseSeries.density shouldn't die

Author: y-p

pandas/sparse/series.py

@@ -378,7 +378,8 @@ def to_dense(self, sparse_only=False):
 
     @property
     def density(self):
-        return float(len(self.sp_index)) / len(self.index)
+        r = float(self.sp_index.npoints) / float(self.sp_index.length)
+        return r
 
     def astype(self, dtype=None):
         """

pandas/sparse/tests/test_sparse.py

@@ -156,6 +156,14 @@ def test_construct_DataFrame_with_sp_series(self):
         # it works!
         df = DataFrame({'col': self.bseries})
 
+    def test_series_density(self):
+        # GH2803
+        ts = Series(np.random.randn(10))
+        ts[2:-2] = nan
+        sts = ts.to_sparse()
+        density =  sts.density # don't die
+        self.assertEqual(density,4/10.0)
+
     def test_sparse_to_dense(self):
         arr, index = _test_data1()
         series = self.bseries.to_dense()