Struct csvsc::prelude::Reducer

pub struct Reducer { /* fields omitted */ }

An uncomplicated builder of arguments for InputStream’s reduce method.

RowStream::reduce() accepts a vector of Aggregates. Use this struct to define them using the methods listed below.

Example

use csvsc::prelude::*;
use encoding::all::UTF_8;

InputStreamBuilder::from_paths(&["test/assets/1.csv"]).unwrap().build().unwrap()
    .reduce(vec![
        Reducer::with_name("rows").count(),
    ])
    .into_iter();

Implementations

impl Reducer

pub fn with_name(name: &str) -> Reducer

Start building an aggregate by giving it a column name. This column will be present in the output row and will contain the aggregated value.

pub fn count(self) -> Box<dyn Aggregate>

Creates an aggregate that counts all Ok rows of the stream.

Example

Reducer::with_name("rows").count();

pub fn custom<'a, A>(reducer: A) -> Box<dyn Aggregate + 'a> where
    A: Aggregate + 'a, 

A custom reducer, this method is not strictrly needed because you can just pass Box::new(YourReducer::new()) to .reduce() but it exists for consistency.

Example

use csvsc::prelude::*;

#[derive(Debug)]
struct MyAggregate {
    colname: String,
    state: (f64, f64),
}

impl Aggregate for MyAggregate {
    fn update(&mut self, headers: &Headers, row: &Row) -> csvsc::error::Result<()> {
        let x: f64 = headers.get_field(row, "x").unwrap().parse().unwrap();
        let y: f64 = headers.get_field(row, "y").unwrap().parse().unwrap();

        self.state.0 += x;
        self.state.1 += y;

        Ok(())
    }

    fn colname(&self) -> &str {
        &self.colname
    }

    fn value(&self) -> String {
        format!("{},{}", self.state.0, self.state.1)
    }
}

Reducer::custom(MyAggregate {
    colname: String::from("custom"),
    state: (0.0, 0.0),
});

pub fn of_column(self, name: &str) -> Reducer

Most aggregates need a source column, use this string as source column name.

Example

Reducer::with_name("richest").of_column("income").max(0.0);

pub fn average(self) -> Option<Box<dyn Aggregate>>

Compute the average of the values in the specified column, if a value cannot be parsed to f64 returns an error row.

Example

Reducer::with_name("average").of_column("income").average();

pub fn last(self, init: &str) -> Option<Box<dyn Aggregate>>

A simple reducer that takes the last value it sees or uses the argument given as default.

Useful for just keeping a column used for grouping in an aggregate.

Example

Reducer::with_name("name").of_column("name").last("-");

pub fn max<'a, T>(self, init: T) -> Option<Box<dyn Aggregate + 'a>> where
    T: Display + Debug + PartialOrd + FromStr + Copy + 'a,
    <T as FromStr>::Err: Debug, 

Return the maximum of the specified column’s values and use init as default if the value cannot be parsed to T.

init is both used to specify the type to parse to and the default. A sensible value for it would be a number smaller than all the values you expect from your data

Example

use std::f64;

Reducer::with_name("max").of_column("height").max(f64::NEG_INFINITY);

pub fn min<'a, T>(self, init: T) -> Option<Box<dyn Aggregate + 'a>> where
    T: Display + Debug + PartialOrd + FromStr + Copy + 'a,
    <T as FromStr>::Err: Debug, 

Return the minimum of the specified column’s values and use init as default if the value cannot be parsed to T.

init is both used to specify the type to parse to and the default. A sensible value for it would be a number higher than all the values you expect from your data.

Example

use std::f64;

Reducer::with_name("min").of_column("height").min(f64::INFINITY);

pub fn sum<'a, T>(self, init: T) -> Option<Box<dyn Aggregate + 'a>> where
    T: Display + Debug + AddAssign + FromStr + Copy + 'a,
    <T as FromStr>::Err: Debug, 

Return the sum of the specified column’s values and use init as default if the value cannot be parsed to T.

init is both used to specify the type to parse to and the default. A sensible value for it would be 0.0

Example

Reducer::with_name("sum").of_column("height").sum(0.0);

pub fn mul<'a, T>(self, init: T) -> Option<Box<dyn Aggregate + 'a>> where
    T: Display + Debug + MulAssign + FromStr + Copy + 'a,
    <T as FromStr>::Err: Debug, 

Return the product of the specified column’s values and use init as default if the value cannot be parsed to T.

init is both used to specify the type to parse to and the default. A sensible value for it would be 1.0

Example

Reducer::with_name("product").of_column("height").mul(1.0);

pub fn with_closure<'a, F, C>(
    self,
    f: F,
    init: C
) -> Option<Box<dyn Aggregate + 'a>> where
    F: FnMut(C, &str) -> Result<C> + 'a,
    C: Display + 'a, 

Use a closure to compute an aggregate for the specified column.

Here you have absolute freedom.

The first argument of the closure is the accumulator, the second is the current row’s value. init will be used as starter.

Example

Reducer::with_name("closure").of_column("col").with_closure(|acc, cur| {
    Ok(acc + cur.parse::<i32>().unwrap())
}, 0).unwrap();