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

// 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.

//! Defines physical expression for `cume_dist` that can evaluated
//! at runtime during query execution

use crate::window::partition_evaluator::PartitionEvaluator;
use crate::window::BuiltInWindowFunctionExpr;
use crate::PhysicalExpr;
use arrow::array::ArrayRef;
use arrow::array::Float64Array;
use arrow::datatypes::{DataType, Field};
use datafusion_common::Result;
use std::any::Any;
use std::iter;
use std::ops::Range;
use std::sync::Arc;

/// CumeDist calculates the cume_dist in the window function with order by
#[derive(Debug)]
pub struct CumeDist {
    name: String,
}

/// Create a cume_dist window function
pub fn cume_dist(name: String) -> CumeDist {
    CumeDist { name }
}

impl BuiltInWindowFunctionExpr for CumeDist {
    /// Return a reference to Any that can be used for downcasting
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn field(&self) -> Result<Field> {
        let nullable = false;
        let data_type = DataType::Float64;
        Ok(Field::new(self.name(), data_type, nullable))
    }

    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> {
        vec![]
    }

    fn name(&self) -> &str {
        &self.name
    }

    fn create_evaluator(&self) -> Result<Box<dyn PartitionEvaluator>> {
        Ok(Box::new(CumeDistEvaluator {}))
    }
}

#[derive(Debug)]
pub(crate) struct CumeDistEvaluator;

impl PartitionEvaluator for CumeDistEvaluator {
    fn include_rank(&self) -> bool {
        true
    }

    fn evaluate_with_rank(
        &self,
        num_rows: usize,
        ranks_in_partition: &[Range<usize>],
    ) -> Result<ArrayRef> {
        let scalar = num_rows as f64;
        let result = Float64Array::from_iter_values(
            ranks_in_partition
                .iter()
                .scan(0_u64, |acc, range| {
                    let len = range.end - range.start;
                    *acc += len as u64;
                    let value: f64 = (*acc as f64) / scalar;
                    let result = iter::repeat(value).take(len);
                    Some(result)
                })
                .flatten(),
        );
        Ok(Arc::new(result))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use datafusion_common::cast::as_float64_array;

    fn test_i32_result(
        expr: &CumeDist,
        num_rows: usize,
        ranks: Vec<Range<usize>>,
        expected: Vec<f64>,
    ) -> Result<()> {
        let result = expr
            .create_evaluator()?
            .evaluate_with_rank(num_rows, &ranks)?;
        let result = as_float64_array(&result)?;
        let result = result.values();
        assert_eq!(expected, result);
        Ok(())
    }

    #[test]
    fn test_cume_dist() -> Result<()> {
        let r = cume_dist("arr".into());

        let expected = vec![0.0; 0];
        test_i32_result(&r, 0, vec![], expected)?;

        let expected = vec![1.0; 1];
        test_i32_result(&r, 1, vec![0..1], expected)?;

        let expected = vec![1.0; 2];
        test_i32_result(&r, 2, vec![0..2], expected)?;

        let expected = vec![0.5, 0.5, 1.0, 1.0];
        test_i32_result(&r, 4, vec![0..2, 2..4], expected)?;

        let expected = vec![0.25, 0.5, 0.75, 1.0];
        test_i32_result(&r, 4, vec![0..1, 1..2, 2..3, 3..4], expected)?;

        Ok(())
    }
}