struct rename fields (#2845)

polars/polars-lazy/src/dsl/struct_.rs

@@ -4,6 +4,7 @@ use super::*;
 pub struct StructNameSpace(pub(crate) Expr);
 
 impl StructNameSpace {
+    /// Retrieve one of the fields of this [`StructChunked`] as a new Series.
     pub fn field_by_name(self, name: &str) -> Expr {
         let name1 = name.to_string();
         let name2 = name.to_string();
@@ -29,4 +30,39 @@ impl StructNameSpace {
             .with_fmt("struct.field_by_name")
             .alias(name)
     }
+
+    /// Rename the fields of the [`StructChunked`].
+    pub fn rename_fields(self, names: Vec<String>) -> Expr {
+        let names = Arc::new(names);
+        let names2 = names.clone();
+        self.0
+            .map(
+                move |s| {
+                    let ca = s.struct_()?;
+                    let fields = ca
+                        .fields()
+                        .iter()
+                        .zip(names.as_ref())
+                        .map(|(s, name)| {
+                            let mut s = s.clone();
+                            s.rename(name);
+                            s
+                        })
+                        .collect::<Vec<_>>();
+                    StructChunked::new(ca.name(), &fields).map(|ca| ca.into_series())
+                },
+                GetOutput::map_dtype(move |dt| match dt {
+                    DataType::Struct(fields) => {
+                        let fields = fields
+                            .iter()
+                            .zip(names2.as_ref())
+                            .map(|(fld, name)| Field::new(name, fld.data_type().clone()))
+                            .collect();
+                        DataType::Struct(fields)
+                    }
+                    _ => dt.clone(),
+                }),
+            )
+            .with_fmt("struct.rename_fields")
+    }
 }

py-polars/docs/source/reference/expression.rst

@@ -354,3 +354,4 @@ The following methods are available under the `expr.struct` attribute.
    :toctree: api/
 
     ExprStructNameSpace.field
+    ExprStructNameSpace.rename_fields

py-polars/docs/source/reference/series.rst

@@ -318,3 +318,4 @@ The following methods are available under the `Series.struct` attribute.
     StructNameSpace.to_frame
     StructNameSpace.field
     StructNameSpace.fields
+    StructNameSpace.rename_fields

py-polars/polars/internals/expr.py

@@ -2847,6 +2847,17 @@ def field(self, name: str) -> Expr:
         """
         return wrap_expr(self._pyexpr.struct_field_by_name(name))
 
+    def rename_fields(self, names: List[str]) -> Expr:
+        """
+        Rename the fields of the struct
+
+        Parameters
+        ----------
+        names
+            New names in the order of the struct's fields
+        """
+        return wrap_expr(self._pyexpr.struct_rename_fields(names))
+
 
 class ExprListNameSpace:
     """

py-polars/polars/internals/series.py

@@ -3560,12 +3560,24 @@ def field(self, name: str) -> Series:
         """
         return pli.select(pli.lit(self.s).struct.field(name)).to_series()
 
+    @property
     def fields(self) -> List[str]:
         """
         Get the names of the fields
         """
         return self.s._s.struct_fields()
 
+    def rename_fields(self, names: List[str]) -> Series:
+        """
+        Rename the fields of the struct
+
+        Parameters
+        ----------
+        names
+            New names in the order of the struct's fields
+        """
+        return pli.select(pli.lit(self.s).struct.rename_fields(names)).to_series()
+
 
 class StringNameSpace:
     """

py-polars/src/lazy/dsl.rs

@@ -1267,6 +1267,10 @@ impl PyExpr {
     pub fn struct_field_by_name(&self, name: &str) -> PyExpr {
         self.inner.clone().struct_().field_by_name(name).into()
     }
+
+    pub fn struct_rename_fields(&self, names: Vec<String>) -> PyExpr {
+        self.inner.clone().struct_().rename_fields(names).into()
+    }
 }
 
 impl From<dsl::Expr> for PyExpr {

py-polars/tests/test_struct.py

@@ -7,7 +7,7 @@ def test_struct_various() -> None:
     )
     s = df.to_struct("my_struct")
 
-    assert s.struct.fields() == ["int", "str", "bool", "list"]
+    assert s.struct.fields == ["int", "str", "bool", "list"]
     assert s[0] == (1, "a", True, pl.Series([1, 2]))
     assert s[1] == (2, "b", None, pl.Series([3]))
     assert s.struct.field("list").to_list() == [[1, 2], [3]]
@@ -43,3 +43,11 @@ def test_apply_to_struct() -> None:
     )
 
     assert df.frame_equal(expected)
+
+
+def test_rename_fields() -> None:
+    df = pl.DataFrame({"int": [1, 2], "str": ["a", "b"], "bool": [True, None]})
+    assert df.to_struct("my_struct").struct.rename_fields(["a", "b"]).struct.fields == [
+        "a",
+        "b",
+    ]