use super::variance::compute_variance as variance;
use crate::math::utils::run_with_function;
use nu_engine::CallExt;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{
record, Category, Example, PipelineData, ShellError, Signature, Span, Type, Value,
};
#[derive(Clone)]
pub struct SubCommand;
impl Command for SubCommand {
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::Table(vec![]), Type::Record(vec![])),
(Type::Record(vec![]), Type::Record(vec![])),
])
.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 usage(&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 run(
&self,
engine_state: &EngineState,
stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<PipelineData, ShellError> {
let sample = call.has_flag(engine_state, stack, "sample")?;
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| {
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(SubCommand {})
}
}