nu_command/math/
median.rs

1use crate::math::{avg::average, utils::run_with_function};
2use nu_engine::command_prelude::*;
3use std::cmp::Ordering;
4
5#[derive(Clone)]
6pub struct MathMedian;
7
8impl Command for MathMedian {
9    fn name(&self) -> &str {
10        "math median"
11    }
12
13    fn signature(&self) -> Signature {
14        Signature::build("math median")
15            .input_output_types(vec![
16                (Type::List(Box::new(Type::Number)), Type::Number),
17                (Type::List(Box::new(Type::Duration)), Type::Duration),
18                (Type::List(Box::new(Type::Filesize)), Type::Filesize),
19                (Type::Range, Type::Number),
20                (Type::table(), Type::record()),
21                (Type::record(), Type::record()),
22            ])
23            .allow_variants_without_examples(true)
24            .category(Category::Math)
25    }
26
27    fn description(&self) -> &str {
28        "Computes the median of a list of numbers."
29    }
30
31    fn search_terms(&self) -> Vec<&str> {
32        vec!["middle", "statistics"]
33    }
34
35    fn is_const(&self) -> bool {
36        true
37    }
38
39    fn run(
40        &self,
41        _engine_state: &EngineState,
42        _stack: &mut Stack,
43        call: &Call,
44        input: PipelineData,
45    ) -> Result<PipelineData, ShellError> {
46        run_with_function(call, input, median)
47    }
48
49    fn run_const(
50        &self,
51        _working_set: &StateWorkingSet,
52        call: &Call,
53        input: PipelineData,
54    ) -> Result<PipelineData, ShellError> {
55        run_with_function(call, input, median)
56    }
57
58    fn examples(&self) -> Vec<Example<'_>> {
59        vec![
60            Example {
61                description: "Compute the median of a list of numbers.",
62                example: "[3 8 9 12 12 15] | math median",
63                result: Some(Value::test_float(10.5)),
64            },
65            Example {
66                description: "Compute the medians of the columns of a table.",
67                example: "[{a: 1 b: 3} {a: 2 b: -1} {a: -3 b: 5}] | math median",
68                result: Some(Value::test_record(record! {
69                    "a" => Value::test_int(1),
70                    "b" => Value::test_int(3),
71                })),
72            },
73            Example {
74                description: "Find the median of a list of file sizes.",
75                example: "[5KB 10MB 200B] | math median",
76                result: Some(Value::test_filesize(5 * 1_000)),
77            },
78        ]
79    }
80}
81
82enum Pick {
83    MedianAverage,
84    Median,
85}
86
87pub fn median(values: &[Value], span: Span, head: Span) -> Result<Value, ShellError> {
88    let mut sorted = values
89        .iter()
90        .filter(|x| !x.as_float().is_ok_and(f64::is_nan))
91        .collect::<Vec<_>>();
92
93    sorted.sort_by(|a, b| a.partial_cmp(b).unwrap_or(Ordering::Equal));
94
95    let take = if sorted.len().is_multiple_of(2) {
96        Pick::MedianAverage
97    } else {
98        Pick::Median
99    };
100
101    match take {
102        Pick::Median => {
103            let idx = sorted.len() / 2;
104            Ok(sorted
105                .get(idx)
106                .ok_or_else(|| ShellError::UnsupportedInput {
107                    msg: "Empty input".to_string(),
108                    input: "value originates from here".into(),
109                    msg_span: head,
110                    input_span: span,
111                })?
112                .to_owned()
113                .to_owned())
114        }
115        Pick::MedianAverage => {
116            let idx_end = sorted.len() / 2;
117            let idx_start = idx_end - 1;
118
119            let left = sorted
120                .get(idx_start)
121                .ok_or_else(|| ShellError::UnsupportedInput {
122                    msg: "Empty input".to_string(),
123                    input: "value originates from here".into(),
124                    msg_span: head,
125                    input_span: span,
126                })?
127                .to_owned()
128                .to_owned();
129
130            let right = sorted
131                .get(idx_end)
132                .ok_or_else(|| ShellError::UnsupportedInput {
133                    msg: "Empty input".to_string(),
134                    input: "value originates from here".into(),
135                    msg_span: head,
136                    input_span: span,
137                })?
138                .to_owned()
139                .to_owned();
140
141            average(&[left, right], span, head)
142        }
143    }
144}
145
146#[cfg(test)]
147mod test {
148    use super::*;
149
150    #[test]
151    fn test_examples() {
152        use crate::test_examples;
153
154        test_examples(MathMedian {})
155    }
156
157    #[test]
158    fn test_median_with_nan_values() {
159        // Test case: [NaN, NaN, 1.0, 2.0, 3.0, 4.0]
160        // values.len() = 6, sorted = [1.0, 2.0, 3.0, 4.0], sorted.len() = 4
161        // Correct median of [1.0, 2.0, 3.0, 4.0] is (2.0 + 3.0) / 2 = 2.5
162        // Bug: using values.len() would give idx_end = 3, returning avg(3.0, 4.0) = 3.5
163        // Fix: using sorted.len() gives idx_end = 2, returning avg(2.0, 3.0) = 2.5
164        let span = Span::test_data();
165        let values = vec![
166            Value::test_float(f64::NAN),
167            Value::test_float(f64::NAN),
168            Value::test_float(1.0),
169            Value::test_float(2.0),
170            Value::test_float(3.0),
171            Value::test_float(4.0),
172        ];
173
174        let result = median(&values, span, span).unwrap();
175        assert_eq!(result, Value::test_float(2.5));
176    }
177}
nu_command/math/median.rs

nu_command/math/
median.rs
