From 4964930b2c34fd96e0b47083f9e1f7f191ca2bfc Mon Sep 17 00:00:00 2001
From: "Heres, Daniel" <danielheres@gmail.com>
Date: Sat, 23 Jan 2021 12:53:15 +0100
Subject: [PATCH] Add PrimitiveArray::from_value

---
 rust/arrow/src/array/array_primitive.rs | 33 +++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/rust/arrow/src/array/array_primitive.rs b/rust/arrow/src/array/array_primitive.rs
index 3dcb187495f..656433c1243 100644
--- a/rust/arrow/src/array/array_primitive.rs
+++ b/rust/arrow/src/array/array_primitive.rs
@@ -94,6 +94,28 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
         let offset = i + self.offset();
         unsafe { *self.raw_values.as_ptr().add(offset) }
     }
+
+    /// Creates a `PrimitiveArray` with a constant `value` and `size`
+    pub fn from_value(value: T::Native, size: usize) -> Self {
+        let mut val_buf = MutableBuffer::new(
+            size * mem::size_of::<<T as ArrowPrimitiveType>::Native>(),
+        );
+
+        for _ in 0..size {
+            val_buf.push(value);
+        }
+
+        let data = ArrayData::new(
+            T::DATA_TYPE,
+            size,
+            None,
+            None,
+            0,
+            vec![val_buf.into()],
+            vec![],
+        );
+        PrimitiveArray::from(Arc::new(data))
+    }
 }
 
 impl<T: ArrowPrimitiveType> Array for PrimitiveArray<T> {
@@ -820,6 +842,17 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_primitive_from_value() {
+        let arr: PrimitiveArray<Int32Type> = PrimitiveArray::from_value(0, 10);
+        assert_eq!(10, arr.len());
+        assert_eq!(0, arr.null_count());
+        for i in 0..10 {
+            assert_eq!(0, arr.value(i));
+        }
+    }
+
+
     #[test]
     #[should_panic(expected = "PrimitiveArray data should contain a single buffer only \
                                (values buffer)")]