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