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https://github.com/rust-lang-nursery/rust-cookbook
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Adds parallel map-reduce recipe
See #329 * Adds example in `concurrency.md` * Adds links to `intro.md`
This commit is contained in:
Jeff Hajewski
Michał Budzyński
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2 changed files with 62 additions and 0 deletions
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@ -5,6 +5,7 @@
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| [Mutate the elements of an array in parallel][ex-rayon-iter-mut] | [![rayon-badge]][rayon] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Search items using given predicate in parallel][ex-rayon-parallel-search] | [![rayon-badge]][rayon] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Sort a vector in parallel][ex-rayon-parallel-sort] | [![rayon-badge]][rayon] [![rand-badge]][rand] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Map-reduce in parallel][ex-rayon-map-reduce] | [![rayon-badge]][rayon] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Generate jpg thumbnails in parallel][ex-rayon-thumbnails] | [![rayon-badge]][rayon] [![glob-badge]][glob] [![image-badge]][image] | [![cat-concurrency-badge]][cat-concurrency][![cat-filesystem-badge]][cat-filesystem] |
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| [Spawn a short-lived thread][ex-crossbeam-spawn] | [![crossbeam-badge]][crossbeam] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Draw fractal dispatching work to a thread pool][ex-threadpool-fractal] | [![threadpool-badge]][threadpool] [![num-badge]][num] [![num_cpus-badge]][num_cpus] [![image-badge]][image] | [![cat-concurrency-badge]][cat-concurrency][![cat-science-badge]][cat-science][![cat-rendering-badge]][cat-rendering] |
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@ -73,6 +74,61 @@ fn main() {
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}
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```
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[ex-rayon-map-reduce]: #ex-rayon-map-reduce
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<a name="ex-rayon-map-reduce"></a>
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## Map-reduce in parallel
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[![rayon-badge]][rayon] [![cat-concurrency-badge]][cat-concurrency]
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This example uses [`rayon::filter`], [`rayon::map`], and [`rayon::reduce`]
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to calculate the coniditional average age of a vector of `Person` objects.
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[`rayon::filter`] allows us to (in parallel) conditionally include elements from
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a collection that satisfy the given predicate. Similarly, [`rayon::map`] and
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[`rayon::reduce`] allow us to transform the filtered elements via a unary
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operation and reduce them to a single value via a given binary operation,
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respectively. We also show use of [`rayon::sum`], which has the same result as
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the reduce operation in this example.
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```rust
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extern crate rayon;
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use rayon::prelude::*;
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struct Person {
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age: u32,
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}
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fn main() {
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let v: Vec<Person> = vec![
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Person { age: 23 },
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Person { age: 19 },
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Person { age: 42 },
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Person { age: 17 },
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Person { age: 17 },
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Person { age: 31 },
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Person { age: 30 },
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];
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let num_over_30 = v.par_iter().filter(|&x| x.age > 30).count() as f32;
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let sum_over_30 = v.par_iter()
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.map(|x| x.age)
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.filter(|&x| x > 30)
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.reduce(|| 0, |x, y| x + y);
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let alt_sum_30: u32 = v.par_iter()
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.map(|x| x.age)
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.filter(|&x| x > 30)
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.sum();
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let avg_over_30 = sum_over_30 as f32 / num_over_30;
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let alt_avg_over_30 = alt_sum_30 as f32/ num_over_30;
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assert!((avg_over_30 - alt_avg_over_30).abs() < std::f32::EPSILON);
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println!("The average age of people older than 30 is {}", avg_over_30);
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}
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```
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[ex-rayon-parallel-search]: #ex-rayon-parallel-search
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<a name="ex-rayon-parallel-search"></a>
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## Search items using given predicate in parallel
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@ -456,7 +512,11 @@ fn run() -> Result<()> {
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[`par_iter`]: https://docs.rs/rayon/*/rayon/iter/trait.IntoParallelRefIterator.html#tymethod.par_iter
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[`par_iter_mut`]: https://docs.rs/rayon/*/rayon/iter/trait.IntoParallelRefMutIterator.html#tymethod.par_iter_mut
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[`par_sort_unstable`]: https://docs.rs/rayon/*/rayon/slice/trait.ParallelSliceMut.html#method.par_sort_unstable
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[`rayon::filter`]: https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.filter
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[`rayon::find_any`]: https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.find_any
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[`rayon::map`]: https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.map
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[`rayon::reduce`]: https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.reduce
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[`rayon::sum`]: https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.sum
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[`std::find`]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.find
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[`Walkdir::new`]: https://docs.rs/walkdir/1.0.7/walkdir/struct.WalkDir.html#method.new
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@ -69,6 +69,7 @@ community. It needs and welcomes help. For details see
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| [Mutate the elements of an array in parallel][ex-rayon-iter-mut] | [![rayon-badge]][rayon] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Search items using given predicate in parallel][ex-rayon-parallel-search] | [![rayon-badge]][rayon] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Sort a vector in parallel][ex-rayon-parallel-sort] | [![rayon-badge]][rayon] [![rand-badge]][rand] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Map-reduce in parallel][ex-rayon-map-reduce] | [![rayon-badge]][rayon] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Generate jpg thumbnails in parallel][ex-rayon-thumbnails] | [![rayon-badge]][rayon] [![glob-badge]][glob] [![image-badge]][image] | [![cat-concurrency-badge]][cat-concurrency][![cat-filesystem-badge]][cat-filesystem] |
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| [Spawn a short-lived thread][ex-crossbeam-spawn] | [![crossbeam-badge]][crossbeam] | [![cat-concurrency-badge]][cat-concurrency] |
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| [Draw fractal dispatching work to a thread pool][ex-threadpool-fractal] | [![threadpool-badge]][threadpool] [![num-badge]][num] [![num_cpus-badge]][num_cpus] [![image-badge]][image] | [![cat-concurrency-badge]][cat-concurrency][![cat-science-badge]][cat-science][![cat-rendering-badge]][cat-rendering] |
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@ -201,6 +202,7 @@ community. It needs and welcomes help. For details see
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[ex-rand-range]: basics.html#ex-rand-range
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[ex-random-port-tcp]: net.html#ex-random-port-tcp
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[ex-rayon-iter-mut]: concurrency.html#ex-rayon-iter-mut
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[ex-rayon-map-reduce]: concurrency.html#ex-rayon-map-reduce
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[ex-rayon-parallel-search]: concurrency.html#ex-rayon-parallel-search
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[ex-rayon-parallel-sort]: concurrency.html#ex-rayon-parallel-sort
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[ex-rayon-thumbnails]: concurrency.html#ex-rayon-thumbnails
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