perf: Improve accumulate_dataframes_vertical performance

crates/polars-core/src/chunked_array/ops/append.rs

@@ -149,7 +149,15 @@ where
     ///
     /// See also [`extend`](Self::extend) for appends to the underlying memory
     pub fn append(&mut self, other: &Self) -> PolarsResult<()> {
-        self.append_owned(other.clone())
+        update_sorted_flag_before_append::<T>(self, other);
+        let len = self.len();
+        self.length = self
+            .length
+            .checked_add(other.length)
+            .ok_or_else(|| polars_err!(ComputeError: LENGTH_LIMIT_MSG))?;
+        self.null_count += other.null_count;
+        new_chunks(&mut self.chunks, &other.chunks, len);
+        Ok(())
     }
 
     /// Append in place. This is done by adding the chunks of `other` to this [`ChunkedArray`].

crates/polars-core/src/frame/mod.rs

@@ -1168,6 +1168,34 @@ impl DataFrame {
         Ok(self)
     }
 
+    pub fn vstack_mut_owned(&mut self, other: DataFrame) -> PolarsResult<&mut Self> {
+        if self.width() != other.width() {
+            polars_ensure!(
+                self.width() == 0,
+                ShapeMismatch:
+                "unable to append to a DataFrame of width {} with a DataFrame of width {}",
+                self.width(), other.width(),
+            );
+            self.columns = other.columns;
+            self.height = other.height;
+            return Ok(self);
+        }
+
+        self.columns
+            .iter_mut()
+            .zip(other.columns.into_iter())
+            .try_for_each::<_, PolarsResult<_>>(|(left, right)| {
+                ensure_can_extend(&*left, &right)?;
+                let right_name = right.name().clone();
+                left.append_owned(right).map_err(|e| {
+                    e.context(format!("failed to vstack column '{right_name}'").into())
+                })?;
+                Ok(())
+            })?;
+        self.height += other.height;
+        Ok(self)
+    }
+
     /// Concatenate a [`DataFrame`] to this [`DataFrame`]
     ///
     /// If many `vstack` operations are done, it is recommended to call [`DataFrame::align_chunks_par`].

crates/polars-core/src/utils/mod.rs

@@ -815,7 +815,7 @@ where
             return Err(width_mismatch(&acc_df, &df));
         }
 
-        acc_df.vstack_mut(&df)?;
+        acc_df.vstack_mut_owned(df)?;
     }
 
     Ok(acc_df)