From 282ec4b2777a3759ff779da7a58d54ec68880a40 Mon Sep 17 00:00:00 2001
From: Alexander Wunschik <mail@wunschik.it>
Date: Wed, 18 Apr 2018 16:38:40 +0200
Subject: [PATCH] do not normalize datasets with too less data

---
 src/helpers.js       |  2 +-
 test/helpers_spec.js | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/helpers.js b/src/helpers.js
index de1b756..e8d97eb 100644
--- a/src/helpers.js
+++ b/src/helpers.js
@@ -9,7 +9,7 @@ export function weightFunc (d, dmax, degree) {
 export function normalize (referenceArr) {
   const cutoff = Math.ceil(0.1 * referenceArr.length)
   const trimmed_arr = sort(referenceArr).slice(cutoff, referenceArr.length - cutoff)
-  const sd = math.std(trimmed_arr)
+  const sd = trimmed_arr.length > 3 ? math.std(trimmed_arr) : 1
   return function (outputArr) {
     return outputArr.map(val => val / sd)
   }
diff --git a/test/helpers_spec.js b/test/helpers_spec.js
index ede64c9..fa7e477 100644
--- a/test/helpers_spec.js
+++ b/test/helpers_spec.js
@@ -44,10 +44,20 @@ describe('function normalize', function () {
     expect: [44.499, 3.266, 2.858, 2.449, 2.041, 1.633, 1.225, 0.816, 0.408, -40.825]
   }
 
+  const caseTwo = {
+    test: [109, 8, 7],
+    expect: [109, 8, 7]
+  }
+
   it('should return array divided by 10% trimmed sample deviation', function () {
     const normalizedArr = normalize(caseOne.test)(caseOne.test)
     expect(math.round(normalizedArr, 3)).to.eql(caseOne.expect)
   })
+
+  it('should return same array if sample count is too small (lt 4)', function () {
+    const normalizedArr = normalize(caseTwo.test)(caseTwo.test)
+    expect(normalizedArr).to.eql(caseTwo.expect)
+  })
 })
 
 describe('function euclideanDist', function () {