[GitHub] [arrow] jorgecarleitao commented on a change in pull request #8102: ARROW-9902: [Rust] [DataFusion] Add array() built-in function

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jorgecarleitao commented on a change in pull request #8102:
URL: https://github.com/apache/arrow/pull/8102#discussion_r483070474



##########
File path: rust/datafusion/src/physical_plan/array_expressions.rs
##########
@@ -0,0 +1,106 @@
+// 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.
+
+//! Array expressions
+
+use crate::error::{ExecutionError, Result};
+use arrow::array::*;
+use arrow::datatypes::DataType;
+use std::sync::Arc;
+
+macro_rules! downcast_vec {
+    ($ARGS:expr, $ARRAY_TYPE:ident) => {{
+        $ARGS
+            .iter()
+            .map(|e| match e.as_any().downcast_ref::<$ARRAY_TYPE>() {
+                Some(array) => Ok(array),
+                _ => Err(ExecutionError::General("failed to downcast".to_string())),
+            })
+    }};
+}
+
+macro_rules! array {
+    ($ARGS:expr, $ARRAY_TYPE:ident, $BUILDER_TYPE:ident) => {{
+        // downcast all arguments to their common format
+        let args =
+            downcast_vec!($ARGS, $ARRAY_TYPE).collect::<Result<Vec<&$ARRAY_TYPE>>>()?;
+
+        let mut builder = FixedSizeListBuilder::<$BUILDER_TYPE>::new(
+            <$BUILDER_TYPE>::new(args[0].len()),
+            args.len() as i32,
+        );
+        // for each entry in the array
+        for index in 0..args[0].len() {
+            for arg in &args {
+                if arg.is_null(index) {
+                    builder.values().append_null()?;
+                } else {
+                    builder.values().append_value(arg.value(index))?;
+                }
+            }
+            builder.append(true)?;
+        }
+        Ok(Arc::new(builder.finish()))
+    }};
+}
+
+/// put values in an array.
+pub fn array(args: &[ArrayRef]) -> Result<ArrayRef> {
+    // do not accept 0 arguments.
+    if args.len() == 0 {
+        return Err(ExecutionError::InternalError(
+            "array requires at least one argument".to_string(),
+        ));
+    }
+
+    match args[0].data_type() {

Review comment:
       Type coercion should do it, but while adding a test to this, I found a bug in the coercion logic. So, this PR will have to wait a bit until the logic is fixed. Spot-on, @andygrove !




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