Implement describe method (#293)

datafusion/tests/test_dataframe.py

@@ -607,3 +607,27 @@ def test_to_pydict(df):
     pydict = df.to_pydict()
     assert type(pydict) == dict
     assert pydict == {"a": [1, 2, 3], "b": [4, 5, 6], "c": [8, 5, 8]}
+
+
+def test_describe(df):
+
+    # Calculate statistics
+    df = df.describe()
+
+    # Collect the result
+    result = df.to_pydict()
+
+    assert result == {
+        "describe": [
+            "count",
+            "null_count",
+            "mean",
+            "std",
+            "min",
+            "max",
+            "median",
+        ],
+        "a": [3.0, 3.0, 2.0, 1.0, 1.0, 3.0, 2.0],
+        "b": [3.0, 3.0, 5.0, 1.0, 4.0, 6.0, 5.0],
+        "c": [3.0, 3.0, 7.0, 1.7320508075688772, 5.0, 8.0, 8.0],
+    }

src/dataframe.rs

@@ -76,6 +76,13 @@ impl PyDataFrame {
         }
     }
 
+    /// Calculate summary statistics for a DataFrame
+    fn describe(&self, py: Python) -> PyResult<Self> {
+        let df = self.df.as_ref().clone();
+        let stat_df = wait_for_future(py, df.describe())?;
+        Ok(Self::new(stat_df))
+    }
+
     /// Returns the schema from the logical plan
     fn schema(&self) -> PyArrowType<Schema> {
         PyArrowType(self.df.schema().into())