vrl 0.32.0

Vector Remap Language
Documentation 
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use crate::compiler::prelude::*;

fn tally_value(array: Value, value: &Value) -> Resolved {
    let array = array.try_array()?;
    Ok(array.iter().filter(|&v| v == value).count().into())
}

#[derive(Clone, Copy, Debug)]
pub struct TallyValue;

impl Function for TallyValue {
    fn identifier(&self) -> &'static str {
        "tally_value"
    }

    fn usage(&self) -> &'static str {
        "Counts the number of times a specific value appears in the provided array."
    }

    fn category(&self) -> &'static str {
        Category::Enumerate.as_ref()
    }

    fn return_kind(&self) -> u16 {
        kind::INTEGER
    }

    fn examples(&self) -> &'static [Example] {
        &[example! {
            title: "count matching values",
            source: r#"tally_value(["foo", "bar", "foo", "baz"], "foo")"#,
            result: Ok("2"),
        }]
    }

    fn compile(
        &self,
        _state: &state::TypeState,
        _ctx: &mut FunctionCompileContext,
        arguments: ArgumentList,
    ) -> Compiled {
        let array = arguments.required("array");
        let value = arguments.required("value");

        Ok(TallyValueFn { array, value }.as_expr())
    }

    fn parameters(&self) -> &'static [Parameter] {
        const PARAMETERS: &[Parameter] = &[
            Parameter::required("array", kind::ARRAY, "The array to search through."),
            Parameter::required(
                "value",
                kind::ANY,
                "The value to count occurrences of in the array.",
            ),
        ];
        PARAMETERS
    }
}

#[derive(Debug, Clone)]
pub(crate) struct TallyValueFn {
    array: Box<dyn Expression>,
    value: Box<dyn Expression>,
}

impl FunctionExpression for TallyValueFn {
    fn resolve(&self, ctx: &mut Context) -> Resolved {
        let array = self.array.resolve(ctx)?;
        let value = self.value.resolve(ctx)?;

        tally_value(array, &value)
    }

    fn type_def(&self, _: &state::TypeState) -> TypeDef {
        TypeDef::integer().infallible()
    }
}

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

    test_function![
        tally_value => TallyValue;

        default {
            args: func_args![
                array: value!(["bar", "foo", "baz", "foo"]),
                value: value!("foo"),
            ],
            want: Ok(value!(2)),
            tdef: TypeDef::integer().infallible(),
        }
    ];
}