datafusion_functions/core/
named_struct.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
3// distributed with this work for additional information
4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
7// with the License.  You may obtain a copy of the License at
8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing,
12// software distributed under the License is distributed on an
13// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18use arrow::array::StructArray;
19use arrow::datatypes::{DataType, Field, FieldRef, Fields};
20use datafusion_common::{exec_err, internal_err, Result};
21use datafusion_expr::{
22    ColumnarValue, Documentation, ReturnFieldArgs, ScalarFunctionArgs,
23};
24use datafusion_expr::{ScalarUDFImpl, Signature, Volatility};
25use datafusion_macros::user_doc;
26use std::any::Any;
27use std::sync::Arc;
28
29#[user_doc(
30    doc_section(label = "Struct Functions"),
31    description = "Returns an Arrow struct using the specified name and input expressions pairs.",
32    syntax_example = "named_struct(expression1_name, expression1_input[, ..., expression_n_name, expression_n_input])",
33    sql_example = r#"
34For example, this query converts two columns `a` and `b` to a single column with
35a struct type of fields `field_a` and `field_b`:
36```sql
37> select * from t;
38+---+---+
39| a | b |
40+---+---+
41| 1 | 2 |
42| 3 | 4 |
43+---+---+
44> select named_struct('field_a', a, 'field_b', b) from t;
45+-------------------------------------------------------+
46| named_struct(Utf8("field_a"),t.a,Utf8("field_b"),t.b) |
47+-------------------------------------------------------+
48| {field_a: 1, field_b: 2}                              |
49| {field_a: 3, field_b: 4}                              |
50+-------------------------------------------------------+
51```"#,
52    argument(
53        name = "expression_n_name",
54        description = "Name of the column field. Must be a constant string."
55    ),
56    argument(
57        name = "expression_n_input",
58        description = "Expression to include in the output struct. Can be a constant, column, or function, and any combination of arithmetic or string operators."
59    )
60)]
61#[derive(Debug)]
62pub struct NamedStructFunc {
63    signature: Signature,
64}
65
66impl Default for NamedStructFunc {
67    fn default() -> Self {
68        Self::new()
69    }
70}
71
72impl NamedStructFunc {
73    pub fn new() -> Self {
74        Self {
75            signature: Signature::variadic_any(Volatility::Immutable),
76        }
77    }
78}
79
80impl ScalarUDFImpl for NamedStructFunc {
81    fn as_any(&self) -> &dyn Any {
82        self
83    }
84
85    fn name(&self) -> &str {
86        "named_struct"
87    }
88
89    fn signature(&self) -> &Signature {
90        &self.signature
91    }
92
93    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
94        internal_err!(
95            "named_struct: return_type called instead of return_field_from_args"
96        )
97    }
98
99    fn return_field_from_args(&self, args: ReturnFieldArgs) -> Result<FieldRef> {
100        // do not accept 0 arguments.
101        if args.scalar_arguments.is_empty() {
102            return exec_err!(
103                "named_struct requires at least one pair of arguments, got 0 instead"
104            );
105        }
106
107        if args.scalar_arguments.len() % 2 != 0 {
108            return exec_err!(
109                "named_struct requires an even number of arguments, got {} instead",
110                args.scalar_arguments.len()
111            );
112        }
113
114        let names = args
115            .scalar_arguments
116            .iter()
117            .enumerate()
118            .step_by(2)
119            .map(|(i, sv)|
120                sv.and_then(|sv| sv.try_as_str().flatten().filter(|s| !s.is_empty()))
121                .map_or_else(
122                    ||
123                        exec_err!(
124                    "{} requires {i}-th (0-indexed) field name as non-empty constant string",
125                    self.name()
126                ),
127                Ok
128                )
129            )
130            .collect::<Result<Vec<_>>>()?;
131        let types = args
132            .arg_fields
133            .iter()
134            .skip(1)
135            .step_by(2)
136            .map(|f| f.data_type())
137            .collect::<Vec<_>>();
138
139        let return_fields = names
140            .into_iter()
141            .zip(types.into_iter())
142            .map(|(name, data_type)| Ok(Field::new(name, data_type.to_owned(), true)))
143            .collect::<Result<Vec<Field>>>()?;
144
145        Ok(Field::new(
146            self.name(),
147            DataType::Struct(Fields::from(return_fields)),
148            true,
149        )
150        .into())
151    }
152
153    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
154        let DataType::Struct(fields) = args.return_type() else {
155            return internal_err!("incorrect named_struct return type");
156        };
157
158        assert_eq!(
159            fields.len(),
160            args.args.len() / 2,
161            "return type field count != argument count / 2"
162        );
163
164        let values: Vec<ColumnarValue> = args
165            .args
166            .chunks_exact(2)
167            .map(|chunk| chunk[1].clone())
168            .collect();
169        let arrays = ColumnarValue::values_to_arrays(&values)?;
170        Ok(ColumnarValue::Array(Arc::new(StructArray::new(
171            fields.clone(),
172            arrays,
173            None,
174        ))))
175    }
176
177    fn documentation(&self) -> Option<&Documentation> {
178        self.doc()
179    }
180}
datafusion_functions/core/named_struct.rs

datafusion_functions/core/
named_struct.rs
