From de837c0ec5671baf59faae4036a89ca7e082cbad Mon Sep 17 00:00:00 2001
From: Bergmann89 <info@bergmann89.de>
Date: Sat, 7 Nov 2020 21:13:31 +0100
Subject: [PATCH] Implemented 'max' and 'max_by' operation

---
 asparit/src/core/iterator.rs | 55 ++++++++++++++++++++++++++++++
 asparit/src/inner/max.rs     | 65 ++++++++++++++++++++++++++++++++++++
 asparit/src/inner/mod.rs     |  1 +
 3 files changed, 121 insertions(+)
 create mode 100644 asparit/src/inner/max.rs

diff --git a/asparit/src/core/iterator.rs b/asparit/src/core/iterator.rs
index c77bdcd..ce495b0 100644
--- a/asparit/src/core/iterator.rs
+++ b/asparit/src/core/iterator.rs
@@ -20,6 +20,7 @@ use crate::{
         map::Map,
         map_init::MapInit,
         map_with::MapWith,
+        max::{Max, MaxBy},
         min::{Min, MinBy},
         product::Product,
         reduce::{Reduce, ReduceWith},
@@ -1139,6 +1140,60 @@ pub trait ParallelIterator<'a>: Sized + Send {
         MinBy::new(self, operation)
     }
 
+    /// Computes the maximum of all the items in the iterator. If the
+    /// iterator is empty, `None` is returned; otherwise, `Some(max)`
+    /// is returned.
+    ///
+    /// Note that the order in which the items will be reduced is not
+    /// specified, so if the `Ord` impl is not truly associative, then
+    /// the results are not deterministic.
+    ///
+    /// Basically equivalent to `self.reduce_with(|a, b| cmp::max(a, b))`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use rayon::prelude::*;
+    ///
+    /// let a = [45, 74, 32];
+    ///
+    /// assert_eq!(a.par_iter().max(), Some(&74));
+    ///
+    /// let b: [i32; 0] = [];
+    ///
+    /// assert_eq!(b.par_iter().max(), None);
+    /// ```
+    fn max(self) -> Max<Self>
+    where
+        Self::Item: Ord,
+    {
+        Max::new(self)
+    }
+
+    /// Computes the maximum of all the items in the iterator with respect to
+    /// the given comparison function. If the iterator is empty, `None` is
+    /// returned; otherwise, `Some(min)` is returned.
+    ///
+    /// Note that the order in which the items will be reduced is not
+    /// specified, so if the comparison function is not associative, then
+    /// the results are not deterministic.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use rayon::prelude::*;
+    ///
+    /// let a = [-3_i32, 77, 53, 240, -1];
+    ///
+    /// assert_eq!(a.par_iter().max_by(|x, y| x.abs().cmp(&y.abs())), Some(&240));
+    /// ```
+    fn max_by<O>(self, operation: O) -> MaxBy<Self, O>
+    where
+        O: Fn(&Self::Item, &Self::Item) -> Ordering + Clone + Send + Sync + 'a,
+    {
+        MaxBy::new(self, operation)
+    }
+
     /// Creates a fresh collection containing all the elements produced
     /// by this parallel iterator.
     ///
diff --git a/asparit/src/inner/max.rs b/asparit/src/inner/max.rs
new file mode 100644
index 0000000..df7d5f1
--- /dev/null
+++ b/asparit/src/inner/max.rs
@@ -0,0 +1,65 @@
+use std::cmp::{max, Ord, Ordering};
+
+use crate::{Driver, Executor, ParallelIterator};
+
+/* Max */
+
+pub struct Max<X> {
+    iterator: X,
+}
+
+impl<X> Max<X> {
+    pub fn new(iterator: X) -> Self {
+        Self { iterator }
+    }
+}
+
+impl<'a, X, T> Driver<'a, Option<T>> for Max<X>
+where
+    X: ParallelIterator<'a, Item = T>,
+    T: Send + Ord + 'a,
+{
+    fn exec_with<E>(self, executor: E) -> E::Result
+    where
+        E: Executor<'a, Option<T>>,
+    {
+        self.iterator.reduce_with(max).exec_with(executor)
+    }
+}
+
+/* MaxBy */
+
+pub struct MaxBy<X, O> {
+    iterator: X,
+    operation: O,
+}
+
+impl<X, O> MaxBy<X, O> {
+    pub fn new(iterator: X, operation: O) -> Self {
+        Self {
+            iterator,
+            operation,
+        }
+    }
+}
+
+impl<'a, X, O, T> Driver<'a, Option<T>> for MaxBy<X, O>
+where
+    X: ParallelIterator<'a, Item = T>,
+    O: Fn(&T, &T) -> Ordering + Clone + Send + Sync + 'a,
+    T: Send + Ord + 'a,
+{
+    fn exec_with<E>(self, executor: E) -> E::Result
+    where
+        E: Executor<'a, Option<T>>,
+    {
+        let operation = self.operation;
+
+        self.iterator
+            .reduce_with(move |a, b| match operation(&a, &b) {
+                Ordering::Greater => b,
+                _ => a,
+            })
+            .exec_with(executor)
+    }
+}
diff --git a/asparit/src/inner/mod.rs b/asparit/src/inner/mod.rs
index 5ffc150..f671984 100644
--- a/asparit/src/inner/mod.rs
+++ b/asparit/src/inner/mod.rs
@@ -11,6 +11,7 @@ pub mod inspect;
 pub mod map;
 pub mod map_init;
 pub mod map_with;
+pub mod max;
 pub mod min;
 pub mod noop;
 pub mod product;