From 220fa4e5ccf5a20648b18146ccbbd5538889bbc5 Mon Sep 17 00:00:00 2001
From: Dev <dev@noreply.dev.sp-tarkov.com>
Date: Thu, 29 Jun 2023 12:36:11 +0100
Subject: [PATCH] use MathNet lib to calc standard dev when choosing average
 price

---
 .../Helpers/MarketPricesHelper.cs             | 38 +++++++++++++------
 .../Helpers/TarkovDevResponse.cs              |  2 +-
 .../MarketPriceLookup.Common.csproj           |  4 ++
 3 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/MarketPriceLookup.Common/Helpers/MarketPricesHelper.cs b/MarketPriceLookup.Common/Helpers/MarketPricesHelper.cs
index 0b7e95e..ab46ecc 100644
--- a/MarketPriceLookup.Common/Helpers/MarketPricesHelper.cs
+++ b/MarketPriceLookup.Common/Helpers/MarketPricesHelper.cs
@@ -7,6 +7,8 @@ using System.Linq;
 using System.Net.Http;
 using System.Net.Http.Json;
 using System.Text.Json;
+using MathNet.Numerics.Statistics;
+using System.Data;
 
 namespace MarketPriceLookup.Common.Helpers
 {
@@ -101,28 +103,40 @@ namespace MarketPriceLookup.Common.Helpers
         }
 
         /// <summary>
-        /// Get items average flea price from all readings taken over the past 7 days
+        /// Get items average flea price from all readings taken over the past 14 days
         /// </summary>
         /// <param name="item"></param>
         private static int GetAveragedPrice(Item item)
         {
-            var sevenDaysAgoTimestamp = DateTimeOffset.UtcNow.AddDays(-7).ToUnixTimeSeconds();
-            var pricesWithinLast7days = new List<int>();
-            foreach (var historicalPrice in item.historicalPrices)
+            var fourteenDaysAgoTimestamp = DateTimeOffset.UtcNow.AddDays(-14).ToUnixTimeSeconds();
+            var filteredPrices = item.historicalPrices.Where(x => long.Parse(x.timestamp) > fourteenDaysAgoTimestamp).OrderBy(x=> x.price).ToList();
+
+            if (filteredPrices.Count == 0)
             {
-                if (long.Parse(historicalPrice.timestamp) > sevenDaysAgoTimestamp)
-                {
-                    pricesWithinLast7days.Add(historicalPrice.price);
-                }
+                // x day filter means no prices, use all data
+                filteredPrices = item.historicalPrices.ToList();
             }
 
-            if (pricesWithinLast7days.Count == 0)
+            if (filteredPrices.Count == 1)
             {
-                LoggingHelpers.LogError($"No prices found for item {item.name} in last 7 days, using any availible");
-                pricesWithinLast7days.AddRange(item.historicalPrices.Select(x => x.price));
+                return filteredPrices[0].price;
             }
 
-            return (int)Math.Round(pricesWithinLast7days.Average());
+            var prices = filteredPrices.Select(x => (double)x.price).ToArray();
+
+            var avgMean = prices.Average();
+            var standardDev = prices.StandardDeviation();
+
+            var upperCutoff = standardDev * 1.5;
+            var lowerCutoff = standardDev * 2;
+
+            var lowerBound = avgMean - lowerCutoff;
+            var upperBound = avgMean + upperCutoff;
+
+            //var outliers = prices.Where(x => x < lowerBound || x > upperBound).ToList();
+            var pricesWithOutliersRemoved = prices.Where(x => x >= lowerBound && x <= upperBound).ToList();
+
+            return (int)Math.Round(pricesWithOutliersRemoved.Average());
         }
 
         public static Prices GetItemPrice(string key)
diff --git a/MarketPriceLookup.Common/Helpers/TarkovDevResponse.cs b/MarketPriceLookup.Common/Helpers/TarkovDevResponse.cs
index ed3689f..a74a760 100644
--- a/MarketPriceLookup.Common/Helpers/TarkovDevResponse.cs
+++ b/MarketPriceLookup.Common/Helpers/TarkovDevResponse.cs
@@ -17,7 +17,7 @@ namespace MarketPriceLookup.Common.Helpers
     {
         public string name { get; set; }
         public int avg24hPrice { get; set; }
-        public double changeLast48hPercent { get; set; }
+        public double? changeLast48hPercent { get; set; }
         public string id { get; set; }
         public HistoricalPrice[] historicalPrices { get; set; }
     }
diff --git a/MarketPriceLookup.Common/MarketPriceLookup.Common.csproj b/MarketPriceLookup.Common/MarketPriceLookup.Common.csproj
index a60e2de..0a9cd21 100644
--- a/MarketPriceLookup.Common/MarketPriceLookup.Common.csproj
+++ b/MarketPriceLookup.Common/MarketPriceLookup.Common.csproj
@@ -4,6 +4,10 @@
     <TargetFramework>net6.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="MathNet.Numerics" Version="5.0.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\MarketPriceLookup.Common.Models\MarketPriceLookup.Common.Models.csproj" />
   </ItemGroup>