invr 0.2.1

Declarative data validation engine using invariants executed on Polars DataFrames.
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

use crate::infrastructure::polars::kind::PolarsKind;
use crate::invariant::Invariant;
use crate::scope::Scope;
use crate::violation::Violation;
use crate::violation::value_object::metric_value::MetricValue;
use polars::prelude::*;

///
/// Builds the Polars expression computing the standard deviation
/// of the target numeric column.
///
/// Scope:
/// - Requires `Scope::Column`
///
/// Behavior:
/// - Casts the column to `Float64`
/// - Computes the sample standard deviation using `std(1)`
///   (delta degrees of freedom = 1)
/// - Returns a single scalar representing the column standard deviation
///
/// The resulting metric represents the raw standard deviation value
/// and is not validated against bounds at this stage.
pub fn plan(inv: &Invariant<PolarsKind>) -> Option<Expr> {
    let Scope::Column { name } = inv.scope() else {
        return None;
    };

    Some(col(name).cast(DataType::Float64).std(1))
}
///
/// Converts the computed standard deviation into a maximum-threshold violation.
///
/// Required parameters:
/// - `max`: maximum allowed standard deviation (float)
///
/// Logic:
/// - Reads the computed `std` value
/// - Returns a violation if `std > max`
///
/// Produced metric:
/// - `std_dev` (float)
pub fn map(inv: &Invariant<PolarsKind>, value: AnyValue) -> Option<Violation> {
    let std = value.try_extract::<f64>().ok()?;
    let max: f64 = inv.require_param("max").ok()?.parse().ok()?;

    if std > max {
        Some(
            Violation::new(
                inv.id().clone(),
                inv.severity(),
                inv.scope().clone(),
                format!("std deviation {std} exceeds max {max}"),
            )
            .with_metric("std_dev", MetricValue::Float(std)),
        )
    } else {
        None
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::domain::invariant::value_object::id::InvariantId;
    use crate::infrastructure::polars::kind::PolarsKind;
    use std::collections::BTreeMap;

    fn make_invariant(column: &str, max: f64) -> Invariant<PolarsKind> {
        let id = InvariantId::new("stddev_max_test").unwrap();
        let mut params = BTreeMap::new();
        params.insert("max".to_string(), max.to_string());

        Invariant::new(
            id,
            PolarsKind::StdDevMax,
            Scope::Column {
                name: column.to_string(),
            },
        )
        .with_params(params)
    }

    fn df(values: Vec<i32>) -> DataFrame {
        let series = Series::new(PlSmallStr::from("a"), values);
        DataFrame::new_infer_height(vec![series.into()]).unwrap()
    }

    #[test]
    fn test_plan_returns_expr() {
        let inv = make_invariant("a", 10.0);
        let expr = plan(&inv);
        assert!(expr.is_some());
    }

    #[test]
    fn test_stddev_no_violation() {
        let df = df(vec![10, 11, 9]);
        let inv = make_invariant("a", 5.0);

        let result = df.lazy().select([plan(&inv).unwrap()]).collect().unwrap();

        let value = result.columns()[0].get(0).unwrap();
        let violation = map(&inv, value);

        assert!(violation.is_none());
    }

    #[test]
    fn test_stddev_violation() {
        let df = df(vec![0, 100, 200]);
        let inv = make_invariant("a", 10.0);

        let result = df.lazy().select([plan(&inv).unwrap()]).collect().unwrap();

        let value = result.columns()[0].get(0).unwrap();
        let violation = map(&inv, value);

        assert!(violation.is_some());
    }

    #[test]
    fn test_wrong_scope_returns_none() {
        let id = InvariantId::new("wrong_scope").unwrap();
        let inv = Invariant::new(id, PolarsKind::StdDevMax, Scope::Dataset);

        let expr = plan(&inv);
        assert!(expr.is_none());
    }
}