Added support for Decimal in build_compare (#998)

src/array/ord.rs

@@ -211,6 +211,7 @@ pub fn build_compare(left: &dyn Array, right: &dyn Array) -> Result<DynComparato
         | (Duration(Nanosecond), Duration(Nanosecond)) => compare_primitives::<i64>(left, right),
         (Float32, Float32) => compare_f32(left, right),
         (Float64, Float64) => compare_f64(left, right),
+        (Decimal(_, _), Decimal(_, _)) => compare_primitives::<i128>(left, right),
         (Utf8, Utf8) => compare_string::<i32>(left, right),
         (LargeUtf8, LargeUtf8) => compare_string::<i64>(left, right),
         (Binary, Binary) => compare_binary::<i32>(left, right),

tests/it/array/ord.rs

@@ -2,6 +2,7 @@ use std::cmp::Ordering;
 
 use arrow2::array::ord::build_compare;
 use arrow2::array::*;
+use arrow2::datatypes::DataType;
 use arrow2::error::Result;
 
 #[test]
@@ -67,6 +68,19 @@ fn f64_zeros() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn decimal() -> Result<()> {
+    let array = Int128Array::from_slice(&[1, 2]).to(DataType::Decimal(38, 0));
+
+    let cmp = build_compare(&array, &array)?;
+
+    assert_eq!(Ordering::Less, (cmp)(0, 1));
+    assert_eq!(Ordering::Equal, (cmp)(1, 1));
+    assert_eq!(Ordering::Greater, (cmp)(1, 0));
+
+    Ok(())
+}
+
 #[test]
 fn dict_utf8() -> Result<()> {
     let data = vec!["a", "b", "c", "a", "a", "c", "c"];