nushell/crates/nu-command/src/math/variance.rs

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use crate::math::utils::run_with_function;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, Span, Value};
#[derive(Clone)]
pub struct SubCommand;
impl Command for SubCommand {
fn name(&self) -> &str {
"math variance"
}
fn signature(&self) -> Signature {
Signature::build("math variance")
.switch("sample", "calculate sample variance", Some('s'))
.category(Category::Math)
}
fn usage(&self) -> &str {
"Finds the variance of a list of numbers or tables"
}
fn run(
&self,
_engine_state: &EngineState,
_stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
let sample = call.has_flag("sample");
run_with_function(call, input, compute_variance(sample))
}
fn examples(&self) -> Vec<Example> {
vec![
Example {
description: "Get the variance of a list of numbers",
example: "echo [1 2 3 4 5] | math variance",
result: Some(Value::Float {
val: 2.0,
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span: Span::test_data(),
}),
},
Example {
description: "Get the sample variance of a list of numbers",
example: "[1 2 3 4 5] | math variance -s",
result: Some(Value::Float {
val: 2.5,
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span: Span::test_data(),
}),
},
]
}
}
fn sum_of_squares(values: &[Value], span: &Span) -> Result<Value, ShellError> {
let n = Value::Int {
val: values.len() as i64,
span: *span,
};
let mut sum_x = Value::Int {
val: 0,
span: *span,
};
let mut sum_x2 = Value::Int {
val: 0,
span: *span,
};
for value in values {
let v = match &value {
Value::Int { .. }
| Value::Float { .. } => {
Ok(value)
},
_ => Err(ShellError::UnsupportedInput(
"Attempted to compute the sum of squared values of a value that cannot be summed or squared.".to_string(),
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value.span().unwrap_or(*span),
))
}?;
let v_squared = &v.mul(*span, v)?;
sum_x2 = sum_x2.add(*span, v_squared)?;
sum_x = sum_x.add(*span, v)?;
}
let sum_x_squared = sum_x.mul(*span, &sum_x)?;
let sum_x_squared_div_n = sum_x_squared.div(*span, &n)?;
let ss = sum_x2.sub(*span, &sum_x_squared_div_n)?;
Ok(ss)
}
pub fn compute_variance(sample: bool) -> impl Fn(&[Value], &Span) -> Result<Value, ShellError> {
move |values: &[Value], span: &Span| {
let n = if sample {
values.len() - 1
} else {
values.len()
};
let sum_of_squares = sum_of_squares(values, span);
let ss = match sum_of_squares {
Err(ShellError::UnsupportedInput(_, err_span)) => Err(ShellError::UnsupportedInput(
"Attempted to compute the variance with an item that cannot be used for that."
.to_string(),
err_span,
)),
other => other,
}?;
let n = Value::Int {
val: n as i64,
span: *span,
};
ss.div(*span, &n)
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_examples() {
use crate::test_examples;
test_examples(SubCommand {})
}
}