From 1df1bb58ff2b3fce02e79e29af543d80d4959ff6 Mon Sep 17 00:00:00 2001
From: Jiayu Liu <Jimexist@users.noreply.github.com>
Date: Wed, 23 Jun 2021 18:56:24 +0800
Subject: [PATCH] concatenating single element array shortcut (#492)

---
 arrow/src/compute/kernels/concat.rs | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arrow/src/compute/kernels/concat.rs b/arrow/src/compute/kernels/concat.rs
index cc976a463ff4..5526432f8d8a 100644
--- a/arrow/src/compute/kernels/concat.rs
+++ b/arrow/src/compute/kernels/concat.rs
@@ -57,6 +57,9 @@ pub fn concat(arrays: &[&Array]) -> Result<ArrayRef> {
         return Err(ArrowError::ComputeError(
             "concat requires input of at least one array".to_string(),
         ));
+    } else if arrays.len() == 1 {
+        let array = arrays[0];
+        return Ok(array.slice(0, array.len()));
     }
 
     if arrays
@@ -113,6 +116,21 @@ mod tests {
         assert!(re.is_err());
     }
 
+    #[test]
+    fn test_concat_one_element_vec() -> Result<()> {
+        let arr = Arc::new(PrimitiveArray::<Int64Type>::from(vec![
+            Some(-1),
+            Some(2),
+            None,
+        ])) as ArrayRef;
+        let result = concat(&[arr.as_ref()])?;
+        assert_eq!(
+            &arr, &result,
+            "concatenating single element array gives back the same result"
+        );
+        Ok(())
+    }
+
     #[test]
     fn test_concat_incompatible_datatypes() {
         let re = concat(&[