nu-command 0.106.0

Nushell's built-in commands
Documentation 
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

use super::variance::compute_variance as variance;
use crate::math::utils::run_with_function;
use nu_engine::command_prelude::*;

#[derive(Clone)]
pub struct MathStddev;

impl Command for MathStddev {
    fn name(&self) -> &str {
        "math stddev"
    }

    fn signature(&self) -> Signature {
        Signature::build("math stddev")
            .input_output_types(vec![
                (Type::List(Box::new(Type::Number)), Type::Number),
                (Type::Range, Type::Number),
                (Type::table(), Type::record()),
                (Type::record(), Type::record()),
            ])
            .switch(
                "sample",
                "calculate sample standard deviation (i.e. using N-1 as the denominator)",
                Some('s'),
            )
            .allow_variants_without_examples(true)
            .category(Category::Math)
    }

    fn description(&self) -> &str {
        "Returns the standard deviation of a list of numbers, or of each column in a table."
    }

    fn search_terms(&self) -> Vec<&str> {
        vec![
            "SD",
            "standard",
            "deviation",
            "dispersion",
            "variation",
            "statistics",
        ]
    }

    fn is_const(&self) -> bool {
        true
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let sample = call.has_flag(engine_state, stack, "sample")?;
        let name = call.head;
        let span = input.span().unwrap_or(name);
        let input: PipelineData = match input.try_expand_range() {
            Err(_) => {
                return Err(ShellError::IncorrectValue {
                    msg: "Range must be bounded".to_string(),
                    val_span: span,
                    call_span: name,
                });
            }
            Ok(val) => val,
        };
        run_with_function(call, input, compute_stddev(sample))
    }

    fn run_const(
        &self,
        working_set: &StateWorkingSet,
        call: &Call,
        input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let sample = call.has_flag_const(working_set, "sample")?;
        let name = call.head;
        let span = input.span().unwrap_or(name);
        let input: PipelineData = match input.try_expand_range() {
            Err(_) => {
                return Err(ShellError::IncorrectValue {
                    msg: "Range must be bounded".to_string(),
                    val_span: span,
                    call_span: name,
                });
            }
            Ok(val) => val,
        };
        run_with_function(call, input, compute_stddev(sample))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Compute the standard deviation of a list of numbers",
                example: "[1 2 3 4 5] | math stddev",
                result: Some(Value::test_float(std::f64::consts::SQRT_2)),
            },
            Example {
                description: "Compute the sample standard deviation of a list of numbers",
                example: "[1 2 3 4 5] | math stddev --sample",
                result: Some(Value::test_float(1.5811388300841898)),
            },
            Example {
                description: "Compute the standard deviation of each column in a table",
                example: "[[a b]; [1 2] [3 4]] | math stddev",
                result: Some(Value::test_record(record! {
                    "a" => Value::test_int(1),
                    "b" => Value::test_int(1),
                })),
            },
        ]
    }
}

pub fn compute_stddev(sample: bool) -> impl Fn(&[Value], Span, Span) -> Result<Value, ShellError> {
    move |values: &[Value], span: Span, head: Span| {
        // variance() produces its own usable error, so we can use `?` to propagated the error.
        let variance = variance(sample)(values, span, head)?;
        let val_span = variance.span();
        match variance {
            Value::Float { val, .. } => Ok(Value::float(val.sqrt(), val_span)),
            Value::Int { val, .. } => Ok(Value::float((val as f64).sqrt(), val_span)),
            other => Ok(other),
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_examples() {
        use crate::test_examples;

        test_examples(MathStddev {})
    }
}