Spark soundex function implementation

datafusion/spark/src/function/string/mod.rs

@@ -25,6 +25,7 @@ pub mod ilike;
 pub mod length;
 pub mod like;
 pub mod luhn_check;
+pub mod soundex;
 pub mod space;
 pub mod substring;
 
@@ -45,6 +46,7 @@ make_udf_function!(format_string::FormatStringFunc, format_string);
 make_udf_function!(space::SparkSpace, space);
 make_udf_function!(substring::SparkSubstring, substring);
 make_udf_function!(base64::SparkUnBase64, unbase64);
+make_udf_function!(soundex::SparkSoundex, soundex);
 
 pub mod expr_fn {
     use datafusion_functions::export_functions;
@@ -110,6 +112,7 @@ pub mod expr_fn {
         "Decodes the input string `str` from a base64 string into binary data.",
         str
     ));
+    export_functions!((soundex, "Returns Soundex code of the string.", str));
 }
 
 pub fn functions() -> Vec<Arc<ScalarUDF>> {
@@ -127,5 +130,6 @@ pub fn functions() -> Vec<Arc<ScalarUDF>> {
         space(),
         substring(),
         unbase64(),
+        soundex(),
     ]
 }

datafusion/spark/src/function/string/soundex.rs

@@ -0,0 +1,138 @@
+// 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 arrow::array::{ArrayRef, OffsetSizeTrait, StringArray};
+use arrow::datatypes::DataType;
+use datafusion::logical_expr::{ColumnarValue, Signature, Volatility};
+use datafusion_common::cast::as_generic_string_array;
+use datafusion_common::utils::take_function_args;
+use datafusion_common::{Result, exec_err};
+use datafusion_expr::{ScalarFunctionArgs, ScalarUDFImpl};
+use datafusion_functions::utils::make_scalar_function;
+use std::any::Any;
+use std::sync::Arc;
+
+/// Spark-compatible `soundex` expression
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#soundex>
+#[derive(Debug, PartialEq, Eq, Hash)]
+pub struct SparkSoundex {
+    signature: Signature,
+}
+
+impl Default for SparkSoundex {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl SparkSoundex {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::string(1, Volatility::Immutable),
+        }
+    }
+}
+
+impl ScalarUDFImpl for SparkSoundex {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "soundex"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
+        Ok(DataType::Utf8)
+    }
+
+    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
+        make_scalar_function(spark_soundex_inner, vec![])(&args.args)
+    }
+}
+
+fn spark_soundex_inner(arg: &[ArrayRef]) -> Result<ArrayRef> {
+    let [array] = take_function_args("soundex", arg)?;
+    match &array.data_type() {
+        DataType::Utf8 => soundex::<i32>(array),
+        DataType::LargeUtf8 => soundex::<i64>(array),
+        other => {
+            exec_err!("unsupported data type {other:?} for function `soundex`")
+        }
+    }
+}
+
+fn soundex<T: OffsetSizeTrait>(array: &ArrayRef) -> Result<ArrayRef> {
+    let str_array = as_generic_string_array::<T>(array)?;
+
+    let result = str_array
+        .iter()
+        .map(|s| s.map(compute_soundex))
+        .collect::<StringArray>();
+
+    Ok(Arc::new(result))
+}
+
+fn compute_soundex(s: &str) -> String {
+    if s.chars().next().is_some_and(|c| c.is_ascii_digit()) {
+        return s.to_string();
+    }
+
+    let mut chars = s.chars().filter(|c| c.is_ascii_alphabetic());
+
+    let first_ch = match chars.next() {
+        Some(c) => c.to_ascii_uppercase(),
+        None => return "".to_string(),
+    };
+
+    let mut result = String::with_capacity(4);
+    result.push(first_ch);
+    let mut last_code = classify_char(first_ch);
+
+    for c in chars {
+        if result.len() >= 4 {
+            break;
+        }
+        let current = classify_char(c);
+        if let Some(digit) = current
+            && current != last_code
+        {
+            result.push(digit);
+        }
+        last_code = current;
+    }
+    while result.len() < 4 {
+        result.push('0');
+    }
+    result
+}
+
+fn classify_char(c: char) -> Option<char> {
+    match c.to_ascii_uppercase() {
+        'B' | 'F' | 'P' | 'V' => Some('1'),
+        'C' | 'G' | 'J' | 'K' | 'Q' | 'S' | 'X' | 'Z' => Some('2'),
+        'D' | 'T' => Some('3'),
+        'L' => Some('4'),
+        'M' | 'N' => Some('5'),
+        'R' => Some('6'),
+        _ => None, // A, E, I, O, U, H, W, Y
+    }
+}

datafusion/sqllogictest/test_files/spark/string/soundex.slt

@@ -15,13 +15,37 @@
 # specific language governing permissions and limitations
 # under the License.
 
-# This file was originally created by a porting script from:
-#   https://github.com/lakehq/sail/tree/43b6ed8221de5c4c4adbedbb267ae1351158b43c/crates/sail-spark-connect/tests/gold_data/function
-# This file is part of the implementation of the datafusion-spark function library.
-# For more information, please see:
-#   https://github.com/apache/datafusion/issues/15914
-
-## Original Query: SELECT soundex('Miller');
-## PySpark 3.5.5 Result: {'soundex(Miller)': 'M460', 'typeof(soundex(Miller))': 'string', 'typeof(Miller)': 'string'}
-#query
-#SELECT soundex('Miller'::string);
+query T
+SELECT soundex('Miller');
+----
+M460
+
+query T
+SELECT soundex(NULL);
+----
+NULL
+
+query T
+SELECT soundex('');
+----
+(empty)
+
+query T
+SELECT soundex('Apache Spark');
+----
+A122
+
+query T
+SELECT soundex('123');
+----
+123
+
+query T
+SELECT soundex('a123');
+----
+A000
+
+query T
+SELECT soundex('Datafusion');
+----
+D312