alamb commented on code in PR #15947:
URL: https://github.com/apache/datafusion/pull/15947#discussion_r2073954485


##########
datafusion/spark/src/function/math/hex.rs:
##########
@@ -0,0 +1,404 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::any::Any;
+use std::sync::Arc;
+
+use crate::function::error_utils::{
+    invalid_arg_count_exec_err, unsupported_data_type_exec_err,
+};
+use arrow::array::{Array, StringArray};
+use arrow::datatypes::DataType;
+use arrow::{
+    array::{as_dictionary_array, as_largestring_array, as_string_array},
+    datatypes::Int32Type,
+};
+use datafusion_common::{
+    cast::{as_binary_array, as_fixed_size_binary_array, as_int64_array},
+    exec_err, DataFusionError,
+};
+use datafusion_expr::Signature;
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, 
Volatility};
+use std::fmt::Write;
+
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#hex>
+#[derive(Debug)]
+pub struct SparkHex {
+    signature: Signature,
+    aliases: Vec<String>,
+}
+
+impl Default for SparkHex {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl SparkHex {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::user_defined(Volatility::Immutable),
+            aliases: vec![],
+        }
+    }
+}
+
+impl ScalarUDFImpl for SparkHex {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "hex"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(
+        &self,
+        _arg_types: &[DataType],
+    ) -> datafusion_common::Result<DataType> {
+        Ok(DataType::Utf8)
+    }
+
+    fn invoke_with_args(
+        &self,
+        args: ScalarFunctionArgs,
+    ) -> datafusion_common::Result<ColumnarValue> {
+        spark_hex(&args.args)
+    }
+
+    fn aliases(&self) -> &[String] {
+        &self.aliases
+    }
+
+    fn coerce_types(
+        &self,
+        arg_types: &[DataType],
+    ) -> datafusion_common::Result<Vec<DataType>> {
+        if arg_types.len() != 1 {
+            return Err(invalid_arg_count_exec_err("hex", (1, 1), 
arg_types.len()));
+        }
+        match &arg_types[0] {
+            DataType::Int64
+            | DataType::Utf8
+            | DataType::LargeUtf8
+            | DataType::Binary
+            | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+            DataType::Dictionary(key_type, value_type) => match 
value_type.as_ref() {
+                DataType::Int64
+                | DataType::Utf8
+                | DataType::LargeUtf8
+                | DataType::Binary
+                | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+                other => {
+                    if other.is_numeric() {
+                        Ok(vec![DataType::Dictionary(
+                            key_type.clone(),
+                            Box::new(DataType::Int64),
+                        )])
+                    } else {
+                        Err(unsupported_data_type_exec_err(
+                            "hex",
+                            "Numeric, String, or Binary",
+                            &arg_types[0],
+                        ))
+                    }
+                }
+            },
+            other => {
+                if other.is_numeric() {
+                    Ok(vec![DataType::Int64])
+                } else {
+                    Err(unsupported_data_type_exec_err(
+                        "hex",
+                        "Numeric, String, or Binary",
+                        &arg_types[0],
+                    ))
+                }
+            }
+        }
+    }
+}
+
+fn hex_int64(num: i64) -> String {
+    format!("{:X}", num)
+}
+
+#[inline(always)]
+fn hex_encode<T: AsRef<[u8]>>(data: T, lower_case: bool) -> String {
+    let mut s = String::with_capacity(data.as_ref().len() * 2);
+    if lower_case {
+        for b in data.as_ref() {
+            // Writing to a string never errors, so we can unwrap here.
+            write!(&mut s, "{b:02x}").unwrap();
+        }
+    } else {
+        for b in data.as_ref() {
+            // Writing to a string never errors, so we can unwrap here.
+            write!(&mut s, "{b:02X}").unwrap();
+        }
+    }
+    s
+}
+
+#[inline(always)]
+fn hex_bytes<T: AsRef<[u8]>>(bytes: T) -> Result<String, std::fmt::Error> {
+    let hex_string = hex_encode(bytes, false);
+    Ok(hex_string)
+}
+
+/// Spark-compatible `hex` function
+pub fn spark_hex(args: &[ColumnarValue]) -> Result<ColumnarValue, 
DataFusionError> {
+    if args.len() != 1 {
+        return Err(DataFusionError::Internal(
+            "hex expects exactly one argument".to_string(),
+        ));
+    }
+
+    let input = match &args[0] {
+        ColumnarValue::Scalar(value) => 
ColumnarValue::Array(value.to_array()?),
+        ColumnarValue::Array(_) => args[0].clone(),
+    };
+
+    match &input {
+        ColumnarValue::Array(array) => match array.data_type() {
+            DataType::Int64 => {
+                let array = as_int64_array(array)?;
+
+                let hexed_array: StringArray =
+                    array.iter().map(|v| v.map(hex_int64)).collect();
+
+                Ok(ColumnarValue::Array(Arc::new(hexed_array)))
+            }
+            DataType::Utf8 => {
+                let array = as_string_array(array);
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::LargeUtf8 => {
+                let array = as_largestring_array(array);
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::Binary => {
+                let array = as_binary_array(array)?;
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::FixedSizeBinary(_) => {
+                let array = as_fixed_size_binary_array(array)?;
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::Dictionary(_, value_type) => {
+                let dict = as_dictionary_array::<Int32Type>(&array);
+
+                let values = match **value_type {
+                    DataType::Int64 => as_int64_array(dict.values())?
+                        .iter()
+                        .map(|v| v.map(hex_int64))
+                        .collect::<Vec<_>>(),
+                    DataType::Utf8 => as_string_array(dict.values())
+                        .iter()
+                        .map(|v| v.map(hex_bytes).transpose())
+                        .collect::<Result<_, _>>()?,
+                    DataType::Binary => as_binary_array(dict.values())?
+                        .iter()
+                        .map(|v| v.map(hex_bytes).transpose())
+                        .collect::<Result<_, _>>()?,
+                    _ => exec_err!(
+                        "hex got an unexpected argument type: {:?}",
+                        array.data_type()
+                    )?,
+                };
+
+                let new_values: Vec<Option<String>> = dict

Review Comment:
   You can likely make this more efficient by avoiding the Strings here and 
reuse the dictionary values
   
   Something like
   ```rust
   let new_dict_array = DictionaryArray::new(dict.keys().clone(), values)
   ```



##########
datafusion/spark/src/function/math/hex.rs:
##########
@@ -0,0 +1,404 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::any::Any;
+use std::sync::Arc;
+
+use crate::function::error_utils::{
+    invalid_arg_count_exec_err, unsupported_data_type_exec_err,
+};
+use arrow::array::{Array, StringArray};
+use arrow::datatypes::DataType;
+use arrow::{
+    array::{as_dictionary_array, as_largestring_array, as_string_array},
+    datatypes::Int32Type,
+};
+use datafusion_common::{
+    cast::{as_binary_array, as_fixed_size_binary_array, as_int64_array},
+    exec_err, DataFusionError,
+};
+use datafusion_expr::Signature;
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, 
Volatility};
+use std::fmt::Write;
+
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#hex>
+#[derive(Debug)]
+pub struct SparkHex {
+    signature: Signature,
+    aliases: Vec<String>,
+}
+
+impl Default for SparkHex {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl SparkHex {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::user_defined(Volatility::Immutable),
+            aliases: vec![],
+        }
+    }
+}
+
+impl ScalarUDFImpl for SparkHex {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "hex"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(
+        &self,
+        _arg_types: &[DataType],
+    ) -> datafusion_common::Result<DataType> {
+        Ok(DataType::Utf8)

Review Comment:
   If this function outputs `Utf8View` it will likely be more performant rather 
than Utf8 



##########
datafusion/spark/src/function/math/hex.rs:
##########
@@ -0,0 +1,404 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::any::Any;
+use std::sync::Arc;
+
+use crate::function::error_utils::{
+    invalid_arg_count_exec_err, unsupported_data_type_exec_err,
+};
+use arrow::array::{Array, StringArray};
+use arrow::datatypes::DataType;
+use arrow::{
+    array::{as_dictionary_array, as_largestring_array, as_string_array},
+    datatypes::Int32Type,
+};
+use datafusion_common::{
+    cast::{as_binary_array, as_fixed_size_binary_array, as_int64_array},
+    exec_err, DataFusionError,
+};
+use datafusion_expr::Signature;
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, 
Volatility};
+use std::fmt::Write;
+
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#hex>
+#[derive(Debug)]
+pub struct SparkHex {
+    signature: Signature,
+    aliases: Vec<String>,
+}
+
+impl Default for SparkHex {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl SparkHex {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::user_defined(Volatility::Immutable),
+            aliases: vec![],
+        }
+    }
+}
+
+impl ScalarUDFImpl for SparkHex {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "hex"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(
+        &self,
+        _arg_types: &[DataType],
+    ) -> datafusion_common::Result<DataType> {
+        Ok(DataType::Utf8)
+    }
+
+    fn invoke_with_args(
+        &self,
+        args: ScalarFunctionArgs,
+    ) -> datafusion_common::Result<ColumnarValue> {
+        spark_hex(&args.args)
+    }
+
+    fn aliases(&self) -> &[String] {
+        &self.aliases
+    }
+
+    fn coerce_types(
+        &self,
+        arg_types: &[DataType],
+    ) -> datafusion_common::Result<Vec<DataType>> {
+        if arg_types.len() != 1 {
+            return Err(invalid_arg_count_exec_err("hex", (1, 1), 
arg_types.len()));
+        }
+        match &arg_types[0] {
+            DataType::Int64
+            | DataType::Utf8
+            | DataType::LargeUtf8
+            | DataType::Binary
+            | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+            DataType::Dictionary(key_type, value_type) => match 
value_type.as_ref() {
+                DataType::Int64
+                | DataType::Utf8
+                | DataType::LargeUtf8
+                | DataType::Binary
+                | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+                other => {
+                    if other.is_numeric() {
+                        Ok(vec![DataType::Dictionary(
+                            key_type.clone(),
+                            Box::new(DataType::Int64),
+                        )])
+                    } else {
+                        Err(unsupported_data_type_exec_err(
+                            "hex",
+                            "Numeric, String, or Binary",
+                            &arg_types[0],
+                        ))
+                    }
+                }
+            },
+            other => {
+                if other.is_numeric() {
+                    Ok(vec![DataType::Int64])
+                } else {
+                    Err(unsupported_data_type_exec_err(
+                        "hex",
+                        "Numeric, String, or Binary",
+                        &arg_types[0],
+                    ))
+                }
+            }
+        }
+    }
+}
+
+fn hex_int64(num: i64) -> String {
+    format!("{:X}", num)
+}
+
+#[inline(always)]
+fn hex_encode<T: AsRef<[u8]>>(data: T, lower_case: bool) -> String {
+    let mut s = String::with_capacity(data.as_ref().len() * 2);
+    if lower_case {
+        for b in data.as_ref() {
+            // Writing to a string never errors, so we can unwrap here.
+            write!(&mut s, "{b:02x}").unwrap();
+        }
+    } else {
+        for b in data.as_ref() {
+            // Writing to a string never errors, so we can unwrap here.
+            write!(&mut s, "{b:02X}").unwrap();
+        }
+    }
+    s
+}
+
+#[inline(always)]
+fn hex_bytes<T: AsRef<[u8]>>(bytes: T) -> Result<String, std::fmt::Error> {
+    let hex_string = hex_encode(bytes, false);
+    Ok(hex_string)
+}
+
+/// Spark-compatible `hex` function
+pub fn spark_hex(args: &[ColumnarValue]) -> Result<ColumnarValue, 
DataFusionError> {
+    if args.len() != 1 {
+        return Err(DataFusionError::Internal(
+            "hex expects exactly one argument".to_string(),
+        ));
+    }
+
+    let input = match &args[0] {
+        ColumnarValue::Scalar(value) => 
ColumnarValue::Array(value.to_array()?),
+        ColumnarValue::Array(_) => args[0].clone(),
+    };
+
+    match &input {
+        ColumnarValue::Array(array) => match array.data_type() {
+            DataType::Int64 => {
+                let array = as_int64_array(array)?;
+
+                let hexed_array: StringArray =

Review Comment:
   You can probably make this much faster by avoiding the allocation by using 
StringBuilder directly
   
   If you are using StringArray something like this:
   
https://docs.rs/arrow/latest/arrow/array/type.GenericStringBuilder.html#example-incrementally-writing-strings-with-stdfmtwrite
   
   
   If you are using StringView I think you'll have to provide a fast path for 
shorter strings and use the StringView builder for longer strings



##########
datafusion/spark/src/function/math/hex.rs:
##########
@@ -0,0 +1,404 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::any::Any;
+use std::sync::Arc;
+
+use crate::function::error_utils::{
+    invalid_arg_count_exec_err, unsupported_data_type_exec_err,
+};
+use arrow::array::{Array, StringArray};
+use arrow::datatypes::DataType;
+use arrow::{
+    array::{as_dictionary_array, as_largestring_array, as_string_array},
+    datatypes::Int32Type,
+};
+use datafusion_common::{
+    cast::{as_binary_array, as_fixed_size_binary_array, as_int64_array},
+    exec_err, DataFusionError,
+};
+use datafusion_expr::Signature;
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, 
Volatility};
+use std::fmt::Write;
+
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#hex>
+#[derive(Debug)]
+pub struct SparkHex {
+    signature: Signature,
+    aliases: Vec<String>,
+}
+
+impl Default for SparkHex {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl SparkHex {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::user_defined(Volatility::Immutable),
+            aliases: vec![],
+        }
+    }
+}
+
+impl ScalarUDFImpl for SparkHex {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "hex"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(
+        &self,
+        _arg_types: &[DataType],
+    ) -> datafusion_common::Result<DataType> {
+        Ok(DataType::Utf8)
+    }
+
+    fn invoke_with_args(
+        &self,
+        args: ScalarFunctionArgs,
+    ) -> datafusion_common::Result<ColumnarValue> {
+        spark_hex(&args.args)
+    }
+
+    fn aliases(&self) -> &[String] {
+        &self.aliases
+    }
+
+    fn coerce_types(
+        &self,
+        arg_types: &[DataType],
+    ) -> datafusion_common::Result<Vec<DataType>> {
+        if arg_types.len() != 1 {
+            return Err(invalid_arg_count_exec_err("expm1", (1, 1), 
arg_types.len()));
+        }
+        match &arg_types[0] {
+            DataType::Int64
+            | DataType::Utf8
+            | DataType::LargeUtf8
+            | DataType::Binary
+            | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+            DataType::Dictionary(key_type, value_type) => match 
value_type.as_ref() {

Review Comment:
   I think it would be simpler if you could use some of the existing signatures 
and then return something for `signature()`:
   
https://github.com/apache/datafusion/blob/a39c07a2338a46fccc1111cafb5a2ffdcf6fd329/datafusion/functions/src/string/to_hex.rs#L116
   
   That way the built in coercion logic would take over. If that doesn't work 
for spark functions, perhaps we can define some spark compatible signatures (as 
in implement `SparkSignature` that would return a 
https://docs.rs/datafusion/latest/datafusion/logical_expr/enum.TypeSignature.html)



##########
datafusion/sqllogictest/test_files/spark/math/hex.slt:
##########
@@ -0,0 +1,26 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+
+#   http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+query T

Review Comment:
   It would be nice to add some array level tests, which is described in 
https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/test_files/spark/README.md



##########
datafusion/spark/src/function/math/hex.rs:
##########
@@ -0,0 +1,404 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::any::Any;
+use std::sync::Arc;
+
+use crate::function::error_utils::{
+    invalid_arg_count_exec_err, unsupported_data_type_exec_err,
+};
+use arrow::array::{Array, StringArray};
+use arrow::datatypes::DataType;
+use arrow::{
+    array::{as_dictionary_array, as_largestring_array, as_string_array},
+    datatypes::Int32Type,
+};
+use datafusion_common::{
+    cast::{as_binary_array, as_fixed_size_binary_array, as_int64_array},
+    exec_err, DataFusionError,
+};
+use datafusion_expr::Signature;
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, 
Volatility};
+use std::fmt::Write;
+
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#hex>
+#[derive(Debug)]
+pub struct SparkHex {
+    signature: Signature,
+    aliases: Vec<String>,
+}
+
+impl Default for SparkHex {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl SparkHex {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::user_defined(Volatility::Immutable),
+            aliases: vec![],
+        }
+    }
+}
+
+impl ScalarUDFImpl for SparkHex {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "hex"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(
+        &self,
+        _arg_types: &[DataType],
+    ) -> datafusion_common::Result<DataType> {
+        Ok(DataType::Utf8)
+    }
+
+    fn invoke_with_args(
+        &self,
+        args: ScalarFunctionArgs,
+    ) -> datafusion_common::Result<ColumnarValue> {
+        spark_hex(&args.args)
+    }
+
+    fn aliases(&self) -> &[String] {
+        &self.aliases
+    }
+
+    fn coerce_types(
+        &self,
+        arg_types: &[DataType],
+    ) -> datafusion_common::Result<Vec<DataType>> {
+        if arg_types.len() != 1 {
+            return Err(invalid_arg_count_exec_err("hex", (1, 1), 
arg_types.len()));
+        }
+        match &arg_types[0] {
+            DataType::Int64
+            | DataType::Utf8
+            | DataType::LargeUtf8
+            | DataType::Binary
+            | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+            DataType::Dictionary(key_type, value_type) => match 
value_type.as_ref() {
+                DataType::Int64
+                | DataType::Utf8
+                | DataType::LargeUtf8
+                | DataType::Binary
+                | DataType::LargeBinary => Ok(vec![arg_types[0].clone()]),
+                other => {
+                    if other.is_numeric() {
+                        Ok(vec![DataType::Dictionary(
+                            key_type.clone(),
+                            Box::new(DataType::Int64),
+                        )])
+                    } else {
+                        Err(unsupported_data_type_exec_err(
+                            "hex",
+                            "Numeric, String, or Binary",
+                            &arg_types[0],
+                        ))
+                    }
+                }
+            },
+            other => {
+                if other.is_numeric() {
+                    Ok(vec![DataType::Int64])
+                } else {
+                    Err(unsupported_data_type_exec_err(
+                        "hex",
+                        "Numeric, String, or Binary",
+                        &arg_types[0],
+                    ))
+                }
+            }
+        }
+    }
+}
+
+fn hex_int64(num: i64) -> String {
+    format!("{:X}", num)
+}
+
+#[inline(always)]
+fn hex_encode<T: AsRef<[u8]>>(data: T, lower_case: bool) -> String {
+    let mut s = String::with_capacity(data.as_ref().len() * 2);
+    if lower_case {
+        for b in data.as_ref() {
+            // Writing to a string never errors, so we can unwrap here.
+            write!(&mut s, "{b:02x}").unwrap();
+        }
+    } else {
+        for b in data.as_ref() {
+            // Writing to a string never errors, so we can unwrap here.
+            write!(&mut s, "{b:02X}").unwrap();
+        }
+    }
+    s
+}
+
+#[inline(always)]
+fn hex_bytes<T: AsRef<[u8]>>(bytes: T) -> Result<String, std::fmt::Error> {
+    let hex_string = hex_encode(bytes, false);
+    Ok(hex_string)
+}
+
+/// Spark-compatible `hex` function
+pub fn spark_hex(args: &[ColumnarValue]) -> Result<ColumnarValue, 
DataFusionError> {
+    if args.len() != 1 {
+        return Err(DataFusionError::Internal(
+            "hex expects exactly one argument".to_string(),
+        ));
+    }
+
+    let input = match &args[0] {
+        ColumnarValue::Scalar(value) => 
ColumnarValue::Array(value.to_array()?),
+        ColumnarValue::Array(_) => args[0].clone(),
+    };
+
+    match &input {
+        ColumnarValue::Array(array) => match array.data_type() {
+            DataType::Int64 => {
+                let array = as_int64_array(array)?;
+
+                let hexed_array: StringArray =
+                    array.iter().map(|v| v.map(hex_int64)).collect();
+
+                Ok(ColumnarValue::Array(Arc::new(hexed_array)))
+            }
+            DataType::Utf8 => {
+                let array = as_string_array(array);
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::LargeUtf8 => {
+                let array = as_largestring_array(array);
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::Binary => {
+                let array = as_binary_array(array)?;
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::FixedSizeBinary(_) => {
+                let array = as_fixed_size_binary_array(array)?;
+
+                let hexed: StringArray = array
+                    .iter()
+                    .map(|v| v.map(hex_bytes).transpose())
+                    .collect::<Result<_, _>>()?;
+
+                Ok(ColumnarValue::Array(Arc::new(hexed)))
+            }
+            DataType::Dictionary(_, value_type) => {
+                let dict = as_dictionary_array::<Int32Type>(&array);
+
+                let values = match **value_type {
+                    DataType::Int64 => as_int64_array(dict.values())?
+                        .iter()
+                        .map(|v| v.map(hex_int64))
+                        .collect::<Vec<_>>(),
+                    DataType::Utf8 => as_string_array(dict.values())
+                        .iter()
+                        .map(|v| v.map(hex_bytes).transpose())
+                        .collect::<Result<_, _>>()?,
+                    DataType::Binary => as_binary_array(dict.values())?
+                        .iter()
+                        .map(|v| v.map(hex_bytes).transpose())
+                        .collect::<Result<_, _>>()?,
+                    _ => exec_err!(
+                        "hex got an unexpected argument type: {:?}",
+                        array.data_type()
+                    )?,
+                };
+
+                let new_values: Vec<Option<String>> = dict

Review Comment:
   You can likely make this more efficient by avoiding the Strings here and 
reuse the dictionary keys with the new values
   
   Something like
   ```rust
   let new_dict_array = DictionaryArray::new(dict.keys().clone(), values)
   ```



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