implement expand at idx for List and Object type

polars/polars-core/src/chunked_array/ops/full.rs

@@ -106,6 +106,18 @@ impl ListChunked {
     }
 }
 
+#[cfg(feature = "object")]
+impl<T: PolarsObject> ChunkFull<T> for ObjectChunked<T> {
+    fn full(name: &str, value: T, length: usize) -> Self
+    where
+        Self: Sized,
+    {
+        let mut ca: Self = (0..length).map(|_| Some(value.clone())).collect();
+        ca.rename(name);
+        ca
+    }
+}
+
 #[cfg(feature = "object")]
 impl<T: PolarsObject> ChunkFullNull for ObjectChunked<T> {
     fn full_null(name: &str, length: usize) -> ObjectChunked<T> {

polars/polars-core/src/chunked_array/ops/mod.rs

@@ -652,15 +652,23 @@ impl ChunkExpandAtIndex<CategoricalType> for CategoricalChunked {
 }
 
 impl ChunkExpandAtIndex<ListType> for ListChunked {
-    fn expand_at_index(&self, _index: usize, _length: usize) -> ListChunked {
-        unimplemented!()
+    fn expand_at_index(&self, index: usize, length: usize) -> ListChunked {
+        let opt_val = self.get(index);
+        match opt_val {
+            Some(val) => ListChunked::full(self.name(), &val, length),
+            None => ListChunked::full_null_with_dtype(self.name(), length, &self.inner_dtype()),
+        }
     }
 }
 
 #[cfg(feature = "object")]
-impl<T> ChunkExpandAtIndex<ObjectType<T>> for ObjectChunked<T> {
-    fn expand_at_index(&self, _index: usize, _length: usize) -> ObjectChunked<T> {
-        todo!()
+impl<T: PolarsObject> ChunkExpandAtIndex<ObjectType<T>> for ObjectChunked<T> {
+    fn expand_at_index(&self, index: usize, length: usize) -> ObjectChunked<T> {
+        let opt_val = self.get(index);
+        match opt_val {
+            Some(val) => ObjectChunked::<T>::full(self.name(), val.clone(), length),
+            None => ObjectChunked::<T>::full_null(self.name(), length),
+        }
     }
 }