Fix quantile

Author: rhshadrach

pandas/core/frame.py

@@ -13059,16 +13059,14 @@ def quantile(
                 interpolation=interpolation,
                 method=method,
             )
-            if method == "single":
-                res = res_df.iloc[0]
-            else:
-                # cannot directly iloc over sparse arrays
-                res = res_df.T.iloc[:, 0]
+            res = res_df.iloc[0]
             if axis == 1 and len(self) == 0:
                 # GH#41544 try to get an appropriate dtype
-                dtype = find_common_type(list(self.dtypes))
-                if needs_i8_conversion(dtype):
-                    return res.astype(dtype)
+                dtype = "float64"
+                cdtype = find_common_type(list(self.dtypes))
+                if needs_i8_conversion(cdtype):
+                    dtype = cdtype
+                return res.astype(dtype)
             return res
 
         q = Index(q, dtype=np.float64)

pandas/tests/frame/methods/test_quantile.py

@@ -658,8 +658,7 @@ def test_quantile_empty_no_rows_floats(self, interp_method):
         tm.assert_frame_equal(res, exp)
 
         res = df.quantile(0.5, axis=1, interpolation=interpolation, method=method)
-        dtype = "float64" if interpolation == "linear" else "object"
-        exp = Series([], index=[], name=0.5, dtype=dtype)
+        exp = Series([], index=[], dtype="float64", name=0.5)
         tm.assert_series_equal(res, exp)
 
         res = df.quantile([0.5], axis=1, interpolation=interpolation, method=method)
@@ -714,8 +713,7 @@ def test_quantile_empty_no_columns(self, interp_method):
         result = df.quantile(
             0.5, numeric_only=True, interpolation=interpolation, method=method
         )
-        dtype = "float64" if interpolation == "linear" else "object"
-        expected = Series([], index=[], name=0.5, dtype=dtype)
+        expected = Series([], index=[], name=0.5, dtype=np.float64)
         expected.index.name = "captain tightpants"
         tm.assert_series_equal(result, expected)