nu_command/math/
stddev.rs

1use super::variance::compute_variance as variance;
2use crate::math::utils::run_with_function;
3use nu_engine::command_prelude::*;
4
5#[derive(Clone)]
6pub struct MathStddev;
7
8impl Command for MathStddev {
9    fn name(&self) -> &str {
10        "math stddev"
11    }
12
13    fn signature(&self) -> Signature {
14        Signature::build("math stddev")
15            .input_output_types(vec![
16                (Type::List(Box::new(Type::Number)), Type::Number),
17                (Type::Range, Type::Number),
18                (Type::table(), Type::record()),
19                (Type::record(), Type::record()),
20            ])
21            .switch(
22                "sample",
23                "calculate sample standard deviation (i.e. using N-1 as the denominator)",
24                Some('s'),
25            )
26            .allow_variants_without_examples(true)
27            .category(Category::Math)
28    }
29
30    fn description(&self) -> &str {
31        "Returns the standard deviation of a list of numbers, or of each column in a table."
32    }
33
34    fn search_terms(&self) -> Vec<&str> {
35        vec![
36            "SD",
37            "standard",
38            "deviation",
39            "dispersion",
40            "variation",
41            "statistics",
42        ]
43    }
44
45    fn is_const(&self) -> bool {
46        true
47    }
48
49    fn run(
50        &self,
51        engine_state: &EngineState,
52        stack: &mut Stack,
53        call: &Call,
54        input: PipelineData,
55    ) -> Result<PipelineData, ShellError> {
56        let sample = call.has_flag(engine_state, stack, "sample")?;
57        let name = call.head;
58        let span = input.span().unwrap_or(name);
59        let input: PipelineData = match input.try_expand_range() {
60            Err(_) => {
61                return Err(ShellError::IncorrectValue {
62                    msg: "Range must be bounded".to_string(),
63                    val_span: span,
64                    call_span: name,
65                });
66            }
67            Ok(val) => val,
68        };
69        run_with_function(call, input, compute_stddev(sample))
70    }
71
72    fn run_const(
73        &self,
74        working_set: &StateWorkingSet,
75        call: &Call,
76        input: PipelineData,
77    ) -> Result<PipelineData, ShellError> {
78        let sample = call.has_flag_const(working_set, "sample")?;
79        let name = call.head;
80        let span = input.span().unwrap_or(name);
81        let input: PipelineData = match input.try_expand_range() {
82            Err(_) => {
83                return Err(ShellError::IncorrectValue {
84                    msg: "Range must be bounded".to_string(),
85                    val_span: span,
86                    call_span: name,
87                });
88            }
89            Ok(val) => val,
90        };
91        run_with_function(call, input, compute_stddev(sample))
92    }
93
94    fn examples(&self) -> Vec<Example> {
95        vec![
96            Example {
97                description: "Compute the standard deviation of a list of numbers",
98                example: "[1 2 3 4 5] | math stddev",
99                result: Some(Value::test_float(std::f64::consts::SQRT_2)),
100            },
101            Example {
102                description: "Compute the sample standard deviation of a list of numbers",
103                example: "[1 2 3 4 5] | math stddev --sample",
104                result: Some(Value::test_float(1.5811388300841898)),
105            },
106            Example {
107                description: "Compute the standard deviation of each column in a table",
108                example: "[[a b]; [1 2] [3 4]] | math stddev",
109                result: Some(Value::test_record(record! {
110                    "a" => Value::test_int(1),
111                    "b" => Value::test_int(1),
112                })),
113            },
114        ]
115    }
116}
117
118pub fn compute_stddev(sample: bool) -> impl Fn(&[Value], Span, Span) -> Result<Value, ShellError> {
119    move |values: &[Value], span: Span, head: Span| {
120        // variance() produces its own usable error, so we can use `?` to propagated the error.
121        let variance = variance(sample)(values, span, head)?;
122        let val_span = variance.span();
123        match variance {
124            Value::Float { val, .. } => Ok(Value::float(val.sqrt(), val_span)),
125            Value::Int { val, .. } => Ok(Value::float((val as f64).sqrt(), val_span)),
126            other => Ok(other),
127        }
128    }
129}
130
131#[cfg(test)]
132mod test {
133    use super::*;
134
135    #[test]
136    fn test_examples() {
137        use crate::test_examples;
138
139        test_examples(MathStddev {})
140    }
141}
nu_command/math/stddev.rs

nu_command/math/
stddev.rs
