From 97cd7b8ad83a2469246da303dbd4d7712ac38a1f Mon Sep 17 00:00:00 2001
From: "Heres, Daniel" <danielheres@gmail.com>
Date: Thu, 8 Sep 2022 18:44:00 +0200
Subject: [PATCH 1/2] Add support for empty projection in RecordBatch::project

---
 arrow/src/record_batch.rs | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arrow/src/record_batch.rs b/arrow/src/record_batch.rs
index 47257b496c1b..a3f494461cb8 100644
--- a/arrow/src/record_batch.rs
+++ b/arrow/src/record_batch.rs
@@ -199,6 +199,16 @@ impl RecordBatch {
 
     /// Projects the schema onto the specified columns
     pub fn project(&self, indices: &[usize]) -> Result<RecordBatch> {
+        if indices.is_empty() {
+            return RecordBatch::try_new_with_options(
+                Arc::new(Schema::empty()),
+                vec![],
+                &RecordBatchOptions {
+                    match_field_names: true,
+                    row_count: Some(self.row_count),
+                },
+            );
+        }
         let projected_schema = self.schema.project(indices)?;
         let batch_fields = indices
             .iter()
@@ -961,6 +971,26 @@ mod tests {
         assert_eq!(expected, record_batch.project(&[0, 2]).unwrap());
     }
 
+    #[test]
+    fn project_empty() {
+        let c: ArrayRef = Arc::new(StringArray::from(vec!["d", "e", "f"]));
+
+        let record_batch =
+            RecordBatch::try_from_iter(vec![("c", c.clone())]).expect("valid conversion");
+
+        let expected = RecordBatch::try_new_with_options(
+            Arc::new(Schema::empty()),
+            vec![],
+            &RecordBatchOptions {
+                match_field_names: true,
+                row_count: Some(3),
+            },
+        )
+        .expect("valid conversion");
+
+        assert_eq!(expected, record_batch.project(&[]).unwrap());
+    }
+
     #[test]
     fn test_no_column_record_batch() {
         let schema = Arc::new(Schema::new(vec![]));

From d51fed88870bb444d9869ab6779830f7b58c8e5b Mon Sep 17 00:00:00 2001
From: "Heres, Daniel" <danielheres@gmail.com>
Date: Thu, 8 Sep 2022 21:15:28 +0200
Subject: [PATCH 2/2] Simplify

---
 arrow/src/record_batch.rs | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/arrow/src/record_batch.rs b/arrow/src/record_batch.rs
index a3f494461cb8..5e7a1d2afbe5 100644
--- a/arrow/src/record_batch.rs
+++ b/arrow/src/record_batch.rs
@@ -199,16 +199,6 @@ impl RecordBatch {
 
     /// Projects the schema onto the specified columns
     pub fn project(&self, indices: &[usize]) -> Result<RecordBatch> {
-        if indices.is_empty() {
-            return RecordBatch::try_new_with_options(
-                Arc::new(Schema::empty()),
-                vec![],
-                &RecordBatchOptions {
-                    match_field_names: true,
-                    row_count: Some(self.row_count),
-                },
-            );
-        }
         let projected_schema = self.schema.project(indices)?;
         let batch_fields = indices
             .iter()
@@ -223,7 +213,14 @@ impl RecordBatch {
             })
             .collect::<Result<Vec<_>>>()?;
 
-        RecordBatch::try_new(SchemaRef::new(projected_schema), batch_fields)
+        RecordBatch::try_new_with_options(
+            SchemaRef::new(projected_schema),
+            batch_fields,
+            &RecordBatchOptions {
+                match_field_names: true,
+                row_count: Some(self.row_count),
+            },
+        )
     }
 
     /// Returns the number of columns in the record batch.