From 032002dce964391e016bf880c894993246aec6eb Mon Sep 17 00:00:00 2001
From: Vasil Nikolov <vaskonikolov2003@gmail.com>
Date: Mon, 24 Apr 2023 01:22:57 +0300
Subject: [PATCH] initial, unoptimized algoritm

---
 src/base/statistics.rs    | 27 +++++++++++++++++++++------
 src/base/variance_test.rs |  2 +-
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/base/statistics.rs b/src/base/statistics.rs
index 9f0e0ee6..bf2c40d8 100644
--- a/src/base/statistics.rs
+++ b/src/base/statistics.rs
@@ -335,12 +335,27 @@ impl<T: Scalar, R: Dim, C: Dim, S: RawStorage<T, R, C>> Matrix<T, R, C, S> {
         if self.is_empty() {
             T::zero()
         } else {
-            let val = self.iter().cloned().fold((T::zero(), T::zero()), |a, b| {
-                (a.0 + b.clone() * b.clone(), a.1 + b)
-            });
-            let denom = T::one() / crate::convert::<_, T>(self.len() as f64);
-            let vd = val.1 * denom.clone();
-            val.0 * denom - vd.clone() * vd
+            // let val = self.iter().cloned().fold((T::zero(), T::zero()), |a, b| {
+            //     (a.0 + b.clone() * b.clone(), a.1 + b)
+            // });
+            // let denom = T::one() / crate::convert::<_, T>(self.len() as f64);
+            // let vd = val.1 * denom.clone();
+            // val.0 * denom - vd.clone() * vd
+            // let mean: T = self.iter().map(|&entry| entry).sum::<T>();
+            //
+            // let x: Vec<T> = (0..1000).map(|_| T::zero()).collect();
+            // let s: T = x.iter().cloned().fold(T::zero(), |a, b| a + b);
+
+            // cannot use sum since `T` is not `Sum` by trait bounds
+            let total_sum = self.iter().cloned().fold(T::zero(), |a, b| a + b);
+            let n_elements = crate::convert::<_, T>(self.len() as f64);
+            let mean = total_sum / n_elements.clone();
+
+            let variance = self.iter().cloned().fold(T::zero(), |acc, x| {
+                acc + (x.clone() - mean.clone()) * (x.clone() - mean.clone())
+            }) / n_elements.clone();
+
+            variance
         }
     }
 
diff --git a/src/base/variance_test.rs b/src/base/variance_test.rs
index eec5f7e4..af5d22af 100644
--- a/src/base/variance_test.rs
+++ b/src/base/variance_test.rs
@@ -2,6 +2,6 @@
 use crate::DVector;
 #[test]
 fn test_variance_new() {
-    let v = DVector::repeat(10_000, 100000000.1234);
+    let v = DVector::repeat(10_000, 100000000.0);
     assert_eq!(v.variance(), 0.0)
 }