From e921413c7486fe68a3511c9bfee133f54ad6e4d6 Mon Sep 17 00:00:00 2001
From: Alex Letkemann <73347343+letkemann@users.noreply.github.com>
Date: Tue, 5 Nov 2024 11:02:59 +0100
Subject: [PATCH 1/2] fix: Copy height in .vstack() for empty dataframes
 (#19641)

---
 crates/polars-core/src/frame/mod.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/crates/polars-core/src/frame/mod.rs b/crates/polars-core/src/frame/mod.rs
index 5c3fcac02207..7f34e7d947fd 100644
--- a/crates/polars-core/src/frame/mod.rs
+++ b/crates/polars-core/src/frame/mod.rs
@@ -1084,6 +1084,7 @@ impl DataFrame {
                 self.width(), other.width(),
             );
             self.columns.clone_from(&other.columns);
+            self.height = other.height;
             return Ok(self);
         }
 
@@ -3567,6 +3568,21 @@ mod test {
         assert_eq!(df.first_col_n_chunks(), 2)
     }
 
+    #[test]
+    fn test_vstack_on_empty_dataframe() {
+        let mut df = DataFrame::empty();    
+    
+        let df_data = df! {
+            "flt" => [1., 1., 2., 2., 3., 3.],
+            "int" => [1, 1, 2, 2, 3, 3, ],
+            "str" => ["a", "a", "b", "b", "c", "c"]
+        }
+        .unwrap();
+
+        df.vstack_mut(&df_data).unwrap();
+        assert_eq!(df.height, 6)
+    }
+
     #[test]
     #[cfg(feature = "zip_with")]
     #[cfg_attr(miri, ignore)]

From c1d485ea8a235212b97ffe40d8320b7ef4f7e8be Mon Sep 17 00:00:00 2001
From: Alex Letkemann <73347343+letkemann@users.noreply.github.com>
Date: Tue, 5 Nov 2024 11:08:55 +0100
Subject: [PATCH 2/2] refactor: formatting

---
 crates/polars-core/src/frame/mod.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/polars-core/src/frame/mod.rs b/crates/polars-core/src/frame/mod.rs
index 7f34e7d947fd..31083f42dfdd 100644
--- a/crates/polars-core/src/frame/mod.rs
+++ b/crates/polars-core/src/frame/mod.rs
@@ -3570,8 +3570,8 @@ mod test {
 
     #[test]
     fn test_vstack_on_empty_dataframe() {
-        let mut df = DataFrame::empty();    
-    
+        let mut df = DataFrame::empty();
+
         let df_data = df! {
             "flt" => [1., 1., 2., 2., 3., 3.],
             "int" => [1, 1, 2, 2, 3, 3, ],