1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153

// 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.

//! [`StringAgg`] accumulator for the `string_agg` function

use arrow::array::ArrayRef;
use arrow_schema::DataType;
use datafusion_common::cast::as_generic_string_array;
use datafusion_common::Result;
use datafusion_common::{not_impl_err, ScalarValue};
use datafusion_expr::function::AccumulatorArgs;
use datafusion_expr::{
    Accumulator, AggregateUDFImpl, Expr, Signature, TypeSignature, Volatility,
};
use std::any::Any;

make_udaf_expr_and_func!(
    StringAgg,
    string_agg,
    expr delimiter,
    "Concatenates the values of string expressions and places separator values between them",
    string_agg_udaf
);

/// STRING_AGG aggregate expression
#[derive(Debug)]
pub struct StringAgg {
    signature: Signature,
}

impl StringAgg {
    /// Create a new StringAgg aggregate function
    pub fn new() -> Self {
        Self {
            signature: Signature::one_of(
                vec![
                    TypeSignature::Exact(vec![DataType::LargeUtf8, DataType::Utf8]),
                    TypeSignature::Exact(vec![DataType::LargeUtf8, DataType::LargeUtf8]),
                    TypeSignature::Exact(vec![DataType::LargeUtf8, DataType::Null]),
                ],
                Volatility::Immutable,
            ),
        }
    }
}

impl Default for StringAgg {
    fn default() -> Self {
        Self::new()
    }
}

impl AggregateUDFImpl for StringAgg {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn name(&self) -> &str {
        "string_agg"
    }

    fn signature(&self) -> &Signature {
        &self.signature
    }

    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
        Ok(DataType::LargeUtf8)
    }

    fn accumulator(&self, acc_args: AccumulatorArgs) -> Result<Box<dyn Accumulator>> {
        match &acc_args.input_exprs[1] {
            Expr::Literal(ScalarValue::Utf8(Some(delimiter)))
            | Expr::Literal(ScalarValue::LargeUtf8(Some(delimiter))) => {
                Ok(Box::new(StringAggAccumulator::new(delimiter)))
            }
            Expr::Literal(ScalarValue::Utf8(None))
            | Expr::Literal(ScalarValue::LargeUtf8(None))
            | Expr::Literal(ScalarValue::Null) => {
                Ok(Box::new(StringAggAccumulator::new("")))
            }
            _ => not_impl_err!(
                "StringAgg not supported for delimiter {}",
                &acc_args.input_exprs[1]
            ),
        }
    }
}

#[derive(Debug)]
pub(crate) struct StringAggAccumulator {
    values: Option<String>,
    delimiter: String,
}

impl StringAggAccumulator {
    pub fn new(delimiter: &str) -> Self {
        Self {
            values: None,
            delimiter: delimiter.to_string(),
        }
    }
}

impl Accumulator for StringAggAccumulator {
    fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
        let string_array: Vec<_> = as_generic_string_array::<i64>(&values[0])?
            .iter()
            .filter_map(|v| v.as_ref().map(ToString::to_string))
            .collect();
        if !string_array.is_empty() {
            let s = string_array.join(self.delimiter.as_str());
            let v = self.values.get_or_insert("".to_string());
            if !v.is_empty() {
                v.push_str(self.delimiter.as_str());
            }
            v.push_str(s.as_str());
        }
        Ok(())
    }

    fn merge_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
        self.update_batch(values)?;
        Ok(())
    }

    fn state(&mut self) -> Result<Vec<ScalarValue>> {
        Ok(vec![self.evaluate()?])
    }

    fn evaluate(&mut self) -> Result<ScalarValue> {
        Ok(ScalarValue::LargeUtf8(self.values.clone()))
    }

    fn size(&self) -> usize {
        std::mem::size_of_val(self)
            + self.values.as_ref().map(|v| v.capacity()).unwrap_or(0)
            + self.delimiter.capacity()
    }
}