Support lower and upper scalar udf on dict arrays

datafusion/functions/src/string/common.rs

@@ -24,7 +24,7 @@ use crate::strings::{
     StringViewArrayBuilder, append_view,
 };
 use arrow::array::{
-    Array, ArrayRef, GenericStringArray, NullBufferBuilder, OffsetSizeTrait,
+    Array, ArrayRef, AsArray, GenericStringArray, NullBufferBuilder, OffsetSizeTrait,
     StringViewArray, new_null_array,
 };
 use arrow::buffer::{Buffer, OffsetBuffer, ScalarBuffer};
@@ -387,6 +387,21 @@ fn case_conversion(
 
                 Ok(ColumnarValue::Array(Arc::new(builder.finish(nulls)?)))
             }
+            DataType::Dictionary(_, _) => {
+                let dict = array.as_any_dictionary();
+                let values = dict.values();
+                let converted = case_conversion(
+                    &[ColumnarValue::Array(Arc::clone(values))],
+                    lower,
+                    name,
+                )?;
+                match converted {
+                    ColumnarValue::Array(new_values) => {
+                        Ok(ColumnarValue::Array(dict.with_values(new_values)))
+                    }
+                    _ => unreachable!("Array input should produce Array output"),
+                }
+            }
             other => exec_err!("Unsupported data type {other:?} for function {name}"),
         },
         ColumnarValue::Scalar(scalar) => match scalar {

datafusion/functions/src/string/lower.rs

@@ -91,7 +91,9 @@ impl ScalarUDFImpl for LowerFunc {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use arrow::array::{Array, ArrayRef, StringArray, StringViewArray};
+    use arrow::array::{
+        Array, ArrayRef, DictionaryArray, StringArray, StringViewArray, UInt8Array,
+    };
     use arrow::datatypes::Field;
     use datafusion_common::config::ConfigOptions;
     use std::sync::Arc;
@@ -370,4 +372,22 @@ mod tests {
         assert_eq!(result_sa.value_data().len(), 10);
         Ok(())
     }
+
+    #[test]
+    fn test_dict() -> Result<()> {
+        let input = Arc::new(DictionaryArray::new(
+            UInt8Array::from_iter_values([0, 1, 1, 0, 1, 0]),
+            Arc::new(StringArray::from_iter_values(["A", "b"])),
+        ));
+
+        let result = invoke_lower(input)?;
+
+        let expected = DictionaryArray::new(
+            UInt8Array::from_iter_values([0, 1, 1, 0, 1, 0]),
+            Arc::new(StringArray::from_iter_values(["a", "b"])),
+        );
+
+        assert_eq!(result.as_ref(), &expected);
+        Ok(())
+    }
 }

datafusion/functions/src/string/upper.rs

@@ -90,7 +90,9 @@ impl ScalarUDFImpl for UpperFunc {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use arrow::array::{Array, ArrayRef, StringArray, StringViewArray};
+    use arrow::array::{
+        Array, ArrayRef, DictionaryArray, StringArray, StringViewArray, UInt8Array,
+    };
     use arrow::datatypes::Field;
     use datafusion_common::config::ConfigOptions;
     use std::sync::Arc;
@@ -369,4 +371,22 @@ mod tests {
         assert_eq!(result_sa.value_data().len(), 10);
         Ok(())
     }
+
+    #[test]
+    fn test_dict() -> Result<()> {
+        let input = Arc::new(DictionaryArray::new(
+            UInt8Array::from_iter_values([0, 1, 1, 0, 1, 0]),
+            Arc::new(StringArray::from_iter_values(["A", "b"])),
+        ));
+
+        let result = invoke_upper(input)?;
+
+        let expected = DictionaryArray::new(
+            UInt8Array::from_iter_values([0, 1, 1, 0, 1, 0]),
+            Arc::new(StringArray::from_iter_values(["A", "B"])),
+        );
+
+        assert_eq!(result.as_ref(), &expected);
+        Ok(())
+    }
 }