From 0d1e1c4f12fa82a1c36e2dd2a41f62c46450564e Mon Sep 17 00:00:00 2001
From: Vinzent Steinberg <Vinzent.Steinberg@gmail.com>
Date: Wed, 24 May 2017 19:16:52 +0200
Subject: [PATCH] Implement `Max`

---
 src/lib.rs    |  2 +-
 src/minmax.rs | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/max.rs  | 34 +++++++++++++++++++++
 3 files changed, 120 insertions(+), 1 deletion(-)
 create mode 100644 tests/max.rs

diff --git a/src/lib.rs b/src/lib.rs
index 8f494b9..0665592 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -41,4 +41,4 @@ mod reduce;
 
 pub use average::{Average, AverageWithError};
 pub use weighted_average::{WeightedAverage, WeightedAverageWithError};
-pub use minmax::Min;
+pub use minmax::{Min, Max};
diff --git a/src/minmax.rs b/src/minmax.rs
index 893427d..e83229c 100644
--- a/src/minmax.rs
+++ b/src/minmax.rs
@@ -7,6 +7,11 @@ fn min(a: f64, b: f64) -> f64 {
     a.min(b)
 }
 
+/// Calculate the maximum of `a` and `b`.
+fn max(a: f64, b: f64) -> f64 {
+    a.max(b)
+}
+
 /// Estimate the minimum of a sequence of numbers ("population").
 ///
 /// Everything is calculated iteratively using constant memory, so the sequence
@@ -86,3 +91,83 @@ impl core::iter::FromIterator<f64> for Min {
         a
     }
 }
+
+/// Estimate the maximum of a sequence of numbers ("population").
+///
+/// Everything is calculated iteratively using constant memory, so the sequence
+/// of numbers can be an iterator.
+///
+///
+/// ## Example
+///
+/// ```
+/// use average::Max;
+///
+/// let a: Max = (1..6).map(Into::into).collect();
+/// assert_eq!(a.max(), 5.);
+/// ```
+#[derive(Debug, Clone)]
+pub struct Max {
+    r: Reduce<fn(f64, f64) -> f64>,
+}
+
+impl Max {
+    /// Create a new maxium estimator from a given value.
+    #[inline]
+    pub fn from_value(x: f64) -> Max {
+        Max {
+            r: Reduce::from_value_and_fn(x, max),
+        }
+    }
+
+    /// Create a new maximum estimator.
+    #[inline]
+    pub fn new() -> Max {
+        Max::from_value(::core::f64::NEG_INFINITY)
+    }
+
+    /// Add an element sampled from the population.
+    #[inline]
+    pub fn add(&mut self, x: f64) {
+        self.r.add(x);
+    }
+
+    /// Estimate the maxium of the population.
+    #[inline]
+    pub fn max(&self) -> f64 {
+        self.r.reduction()
+    }
+
+    /// Merge another sample into this one.
+    ///
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// use average::Max;
+    ///
+    /// let sequence: &[f64] = &[1., 2., 3., 4., 5., 6., 7., 8., 9.];
+    /// let (left, right) = sequence.split_at(3);
+    /// let max_total: Max = sequence.iter().map(|x| *x).collect();
+    /// let mut max_left: Max = left.iter().map(|x| *x).collect();
+    /// let max_right: Max = right.iter().map(|x| *x).collect();
+    /// max_left.merge(&max_right);
+    /// assert_eq!(max_total.max(), max_left.max());
+    /// ```
+    #[inline]
+    pub fn merge(&mut self, other: &Max) {
+        self.r.merge(&other.r);
+    }
+}
+
+impl core::iter::FromIterator<f64> for Max {
+    fn from_iter<T>(iter: T) -> Max
+        where T: IntoIterator<Item=f64>
+    {
+        let mut a = Max::new();
+        for i in iter {
+            a.add(i);
+        }
+        a
+    }
+}
diff --git a/tests/max.rs b/tests/max.rs
new file mode 100644
index 0000000..7ee026e
--- /dev/null
+++ b/tests/max.rs
@@ -0,0 +1,34 @@
+extern crate average;
+
+extern crate core;
+
+use core::iter::Iterator;
+
+use average::Max;
+
+#[test]
+fn trivial() {
+    let mut m = Max::new();
+    m.add(2.);
+    m.add(1.);
+    assert_eq!(m.max(), 2.);
+    m.add(3.);
+    m.add(1.);
+    assert_eq!(m.max(), 3.)
+}
+
+#[test]
+fn merge() {
+    let sequence: &[f64] = &[1., 2., 3., 4., 5., 6., 7., 8., 9.];
+    for mid in 1..sequence.len() {
+        let (left, right) = sequence.split_at(mid);
+        let max_total: Max = sequence.iter().map(|x| *x).collect();
+        assert_eq!(max_total.max(), 9.);
+        let mut max_left: Max = left.iter().map(|x| *x).collect();
+        assert_eq!(max_left.max(), sequence[mid - 1]);
+        let max_right: Max = right.iter().map(|x| *x).collect();
+        assert_eq!(max_right.max(), 9.);
+        max_left.merge(&max_right);
+        assert_eq!(max_total.max(), max_left.max());
+    }
+}