davidlghellin commented on code in PR #20928: URL: https://github.com/apache/datafusion/pull/20928#discussion_r3390490411
########## 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(); Review Comment: Applied. Helpers now take `&mut StringBuilder` and write parts directly via `fmt::Write::write_str`; rows are finalised with `builder.append_value("")`. Confirmed in arrow-rs 58.3.0 `generic_bytes_builder.rs:359-364` that the `Write` impl is just `extend_from_slice` (non-fallible), so `.expect("StringBuilder::write_str is infallible")` documents the contract without a real failure path. Saves one memcpy per row. -- This is an automated message from the Apache Git Service. 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