Function parallel_sum 

pub fn parallel_sum<T, I, F>(items: I, extract: F) -> f64
where
    T: Send,
    I: ParallelIterator<Item = T>,
    F: Fn(&T) -> f64 + Sync + Send,

Sum values extracted from items in parallel.

Example

use grafeo_core::execution::parallel::fold::parallel_sum;
use rayon::prelude::*;

let items = vec![(1, "a"), (2, "b"), (3, "c")];
let sum = parallel_sum(items.par_iter(), |(n, _)| *n as f64);
assert_eq!(sum, 6.0);