davidlghellin commented on code in PR #20928: URL: https://github.com/apache/datafusion/pull/20928#discussion_r3390492794
########## datafusion/spark/src/function/string/concat_ws.rs: ########## @@ -0,0 +1,289 @@ +// 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. + +//! Spark-compatible `concat_ws`: joins strings (and array elements) with a separator. +//! +//! Null scalar args and null array elements are skipped; a null separator yields a +//! null row. Non-string args are coerced to STRING; list args (`List`, `LargeList`, +//! `ListView`, `LargeListView`, `FixedSizeList`) expand their elements. +//! +//! Differences with DataFusion core `concat_ws`: +//! - Accepts list arguments and expands their elements +//! - Always returns Utf8 (Spark's `STRING` type) +//! - Coerces non-string scalars (numbers, booleans, dates, ...) to Utf8 + +use std::sync::Arc; + +use arrow::array::{ + Array, ArrayRef, AsArray, GenericListArray, LargeStringArray, OffsetSizeTrait, + StringArray, StringBuilder, StringViewArray, +}; +use arrow::datatypes::DataType; +use datafusion_common::{Result, ScalarValue}; +use datafusion_expr::{ + ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, Signature, Volatility, +}; + +use crate::function::error_utils::{ + invalid_arg_count_exec_err, unsupported_data_type_exec_err, +}; + +#[derive(Debug, PartialEq, Eq, Hash)] +pub struct SparkConcatWs { + signature: Signature, +} + +impl Default for SparkConcatWs { + fn default() -> Self { + Self::new() + } +} + +impl SparkConcatWs { + pub fn new() -> Self { + Self { + signature: Signature::user_defined(Volatility::Immutable), + } + } +} + +impl ScalarUDFImpl for SparkConcatWs { + fn name(&self) -> &str { + "concat_ws" + } + + fn signature(&self) -> &Signature { + &self.signature + } + + fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> { + Ok(DataType::Utf8) + } + + fn coerce_types(&self, arg_types: &[DataType]) -> Result<Vec<DataType>> { + if arg_types.is_empty() { + return Err(invalid_arg_count_exec_err("concat_ws", (1, i32::MAX), 0)); + } + Ok(arg_types + .iter() + .enumerate() + .map(|(i, dt)| match dt { + DataType::Utf8 | DataType::LargeUtf8 | DataType::Utf8View => dt.clone(), + // Non-separator list args expand their elements at runtime; + // normalize list variants so the kernel only sees List/LargeList. + DataType::List(f) + | DataType::ListView(f) + | DataType::FixedSizeList(f, _) + if i > 0 => + { + DataType::List(Arc::clone(f)) + } + DataType::LargeList(f) | DataType::LargeListView(f) if i > 0 => { + DataType::LargeList(Arc::clone(f)) + } + // Spark casts everything else (numbers, booleans, dates, + // binary, null...) to STRING. + _ => DataType::Utf8, + }) + .collect()) + } + + fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> { + // Only separator provided → empty string (or NULL if separator is null). + // Arg-count validation happens in coerce_types at planning time. + if args.args.len() == 1 { + return only_separator(&args.args[0]); + } + + spark_concat_ws(&args.args, args.number_rows) + } +} + +fn only_separator(sep: &ColumnarValue) -> Result<ColumnarValue> { + match sep { + ColumnarValue::Scalar(s) if s.is_null() => { + Ok(ColumnarValue::Scalar(ScalarValue::Utf8(None))) + } + ColumnarValue::Scalar(_) => Ok(ColumnarValue::Scalar(ScalarValue::Utf8(Some( + String::new(), + )))), + ColumnarValue::Array(arr) => { + let mut builder = StringBuilder::with_capacity(arr.len(), 0); + for row_idx in 0..arr.len() { + if arr.is_null(row_idx) { + builder.append_null(); + } else { + builder.append_value(""); + } + } + Ok(ColumnarValue::Array(Arc::new(builder.finish()) as ArrayRef)) + } + } +} + +fn spark_concat_ws(args: &[ColumnarValue], num_rows: usize) -> Result<ColumnarValue> { + let arrays = ColumnarValue::values_to_arrays(args)?; + + // Untyped-NULL separator → every row is NULL. Returning a scalar is enough; + // the framework broadcasts it to `num_rows` nulls when needed. + if *arrays[0].data_type() == DataType::Null { + return Ok(ColumnarValue::Scalar(ScalarValue::Utf8(None))); + } + + let sep_view = StringView::try_new(&arrays[0])?; + let arg_views: Vec<ArgView> = arrays[1..] + .iter() + .map(ArgView::try_new) + .collect::<Result<_>>()?; + + let mut builder = StringBuilder::with_capacity(num_rows, num_rows * 16); + let mut buf = String::new(); + + for row_idx in 0..num_rows { + if sep_view.is_null(row_idx) { + builder.append_null(); + continue; + } + + let separator = sep_view.value(row_idx); + buf.clear(); + let mut first = true; + + for view in &arg_views { + view.write_row(row_idx, separator, &mut buf, &mut first)?; + } + + builder.append_value(&buf); + } + + Ok(ColumnarValue::Array(Arc::new(builder.finish()) as ArrayRef)) +} + +/// Typed view over a string array that downcasts once and exposes +/// per-row access without further dispatch. +enum StringView<'a> { + Utf8(&'a StringArray), + LargeUtf8(&'a LargeStringArray), + Utf8View(&'a StringViewArray), +} + +impl<'a> StringView<'a> { + fn try_new(arr: &'a ArrayRef) -> Result<Self> { + match arr.data_type() { + DataType::Utf8 => Ok(Self::Utf8(arr.as_string::<i32>())), + DataType::LargeUtf8 => Ok(Self::LargeUtf8(arr.as_string::<i64>())), + DataType::Utf8View => Ok(Self::Utf8View(arr.as_string_view())), + other => Err(unsupported_data_type_exec_err("concat_ws", "STRING", other)), + } + } + + fn value(&self, idx: usize) -> &str { + match self { + Self::Utf8(a) => a.value(idx), + Self::LargeUtf8(a) => a.value(idx), + Self::Utf8View(a) => a.value(idx), + } + } + + fn is_null(&self, idx: usize) -> bool { + match self { + Self::Utf8(a) => a.is_null(idx), + Self::LargeUtf8(a) => a.is_null(idx), + Self::Utf8View(a) => a.is_null(idx), + } + } +} + +/// Per-argument view: a string array, a list of strings, or an all-null +/// argument. The downcast happens once at construction time. +enum ArgView<'a> { + Null, + Str(StringView<'a>), + List(&'a GenericListArray<i32>), + LargeList(&'a GenericListArray<i64>), +} + +impl<'a> ArgView<'a> { + fn try_new(arr: &'a ArrayRef) -> Result<Self> { + match arr.data_type() { + DataType::Null => Ok(Self::Null), + DataType::Utf8 | DataType::LargeUtf8 | DataType::Utf8View => { + Ok(Self::Str(StringView::try_new(arr)?)) + } + DataType::List(_) => Ok(Self::List(arr.as_list::<i32>())), + DataType::LargeList(_) => Ok(Self::LargeList(arr.as_list::<i64>())), + other => Err(unsupported_data_type_exec_err( + "concat_ws", + "STRING or ARRAY<STRING>", + other, + )), + } + } + + fn write_row( + &self, + row_idx: usize, + sep: &str, + buf: &mut String, + first: &mut bool, + ) -> Result<()> { + match self { + Self::Null => {} + Self::Str(view) => { + if !view.is_null(row_idx) { + push_part(buf, view.value(row_idx), sep, first); + } + } + Self::List(list) => write_list_row(*list, row_idx, sep, buf, first)?, + Self::LargeList(list) => write_list_row(*list, row_idx, sep, buf, first)?, + } + Ok(()) + } +} + +fn write_list_row<O: OffsetSizeTrait>( + list: &GenericListArray<O>, + row_idx: usize, + sep: &str, + buf: &mut String, + first: &mut bool, +) -> Result<()> { + if list.is_null(row_idx) { + return Ok(()); + } + let values = list.value(row_idx); + // An empty array (e.g. `array()`) or an all-null-typed array contributes + // nothing — Spark renders it as the empty string, not an error. + if values.is_empty() || *values.data_type() == DataType::Null { + return Ok(()); + } + let view = StringView::try_new(&values)?; Review Comment: Good catch — the guarantee was missing. Fixed by forcing the list field's element type to `Utf8` in `coerce_types`: ```rust DataType::List(f) | DataType::ListView(f) | DataType::FixedSizeList(f, _) if i > 0 => { DataType::List(Arc::new(Field::new(f.name(), DataType::Utf8, f.is_nullable()))) } ``` The planner now inserts a cast on the list elements, so the runtime is guaranteed to receive `List<Utf8>`. Verified against Spark 4.1.1: - `concat_ws(',', array(1,2,3))` → `1,2,3` - `concat_ws('-', array(1.5,2.5,3.5))` → `1.5-2.5-3.5` - `concat_ws(',', array(true,false,true))` → `true,false,true` All match. Added as SLT cases. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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