datafusion_functions/string/
lower.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::datatypes::DataType;
19use std::any::Any;
20
21use crate::string::common::to_lower;
22use crate::utils::utf8_to_str_type;
23use datafusion_common::Result;
24use datafusion_expr::{ColumnarValue, Documentation};
25use datafusion_expr::{ScalarFunctionArgs, ScalarUDFImpl, Signature, Volatility};
26use datafusion_macros::user_doc;
27
28#[user_doc(
29    doc_section(label = "String Functions"),
30    description = "Converts a string to lower-case.",
31    syntax_example = "lower(str)",
32    sql_example = r#"```sql
33> select lower('Ångström');
34+-------------------------+
35| lower(Utf8("Ångström")) |
36+-------------------------+
37| ångström                |
38+-------------------------+
39```"#,
40    standard_argument(name = "str", prefix = "String"),
41    related_udf(name = "initcap"),
42    related_udf(name = "upper")
43)]
44#[derive(Debug)]
45pub struct LowerFunc {
46    signature: Signature,
47}
48
49impl Default for LowerFunc {
50    fn default() -> Self {
51        Self::new()
52    }
53}
54
55impl LowerFunc {
56    pub fn new() -> Self {
57        Self {
58            signature: Signature::string(1, Volatility::Immutable),
59        }
60    }
61}
62
63impl ScalarUDFImpl for LowerFunc {
64    fn as_any(&self) -> &dyn Any {
65        self
66    }
67
68    fn name(&self) -> &str {
69        "lower"
70    }
71
72    fn signature(&self) -> &Signature {
73        &self.signature
74    }
75
76    fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
77        utf8_to_str_type(&arg_types[0], "lower")
78    }
79
80    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
81        to_lower(&args.args, "lower")
82    }
83
84    fn documentation(&self) -> Option<&Documentation> {
85        self.doc()
86    }
87}
88
89#[cfg(test)]
90mod tests {
91    use super::*;
92    use arrow::array::{Array, ArrayRef, StringArray};
93    use std::sync::Arc;
94
95    fn to_lower(input: ArrayRef, expected: ArrayRef) -> Result<()> {
96        let func = LowerFunc::new();
97
98        let args = ScalarFunctionArgs {
99            number_rows: input.len(),
100            args: vec![ColumnarValue::Array(input)],
101            return_type: &DataType::Utf8,
102        };
103
104        let result = match func.invoke_with_args(args)? {
105            ColumnarValue::Array(result) => result,
106            _ => unreachable!("lower"),
107        };
108        assert_eq!(&expected, &result);
109        Ok(())
110    }
111
112    #[test]
113    fn lower_maybe_optimization() -> Result<()> {
114        let input = Arc::new(StringArray::from(vec![
115            Some("农历新年"),
116            None,
117            Some("DATAFUSION"),
118            Some("0123456789"),
119            Some(""),
120        ])) as ArrayRef;
121
122        let expected = Arc::new(StringArray::from(vec![
123            Some("农历新年"),
124            None,
125            Some("datafusion"),
126            Some("0123456789"),
127            Some(""),
128        ])) as ArrayRef;
129
130        to_lower(input, expected)
131    }
132
133    #[test]
134    fn lower_full_optimization() -> Result<()> {
135        let input = Arc::new(StringArray::from(vec![
136            Some("ARROW"),
137            None,
138            Some("DATAFUSION"),
139            Some("0123456789"),
140            Some(""),
141        ])) as ArrayRef;
142
143        let expected = Arc::new(StringArray::from(vec![
144            Some("arrow"),
145            None,
146            Some("datafusion"),
147            Some("0123456789"),
148            Some(""),
149        ])) as ArrayRef;
150
151        to_lower(input, expected)
152    }
153
154    #[test]
155    fn lower_partial_optimization() -> Result<()> {
156        let input = Arc::new(StringArray::from(vec![
157            Some("ARROW"),
158            None,
159            Some("DATAFUSION"),
160            Some("@_"),
161            Some("0123456789"),
162            Some(""),
163            Some("\t\n"),
164            Some("ὈΔΥΣΣΕΎΣ"),
165            Some("TSCHÜSS"),
166            Some("Ⱦ"), // ⱦ: length change
167            Some("农历新年"),
168        ])) as ArrayRef;
169
170        let expected = Arc::new(StringArray::from(vec![
171            Some("arrow"),
172            None,
173            Some("datafusion"),
174            Some("@_"),
175            Some("0123456789"),
176            Some(""),
177            Some("\t\n"),
178            Some("ὀδυσσεύς"),
179            Some("tschüss"),
180            Some("ⱦ"),
181            Some("农历新年"),
182        ])) as ArrayRef;
183
184        to_lower(input, expected)
185    }
186}
datafusion_functions/string/lower.rs

datafusion_functions/string/
lower.rs
