arthernan · March 7, 2014 22:57 · Mar 7, 2014
diff --git a/AboutTheStockExample.fs b/AboutTheStockExample.fs
@@ -0,0 +1,84 @@
+namespace FSharpKoans
+open FSharpKoans.Core
+
+//---------------------------------------------------------------
+// Apply Your Knowledge!
+//
+// Below is a list containing comma separated data about 
+// Microsoft's stock prices during March of 2012. Without
+// modifying the list, programatically find the day with the
+// greatest variance between the opening and closing price.
+//
+// The following functions may be of use:
+// 
+// abs - takes the absolute value of an argument
+// 
+// System.Double.Parse - converts a string argument into a 
+//                       numerical value.
+//
+// The following function will convert a comma separated string
+// into an array of the column values.
+//                       
+// let splitCommas (x:string) =
+//     x.Split([|','|])
+//---------------------------------------------------------------
+
+
+
+[<Koan(Sort = 15)>]
+module ``about the stock example`` =
+
+    let splitCommas (x:string) =
+        x.Split([|','|])
+
+
+    let stockData =
+        [ "Date,Open,High,Low,Close,Volume,Adj Close";
+          "2012-03-30,32.40,32.41,32.04,32.26,31749400,32.26";
+          "2012-03-29,32.06,32.19,31.81,32.12,37038500,32.12";
+          "2012-03-28,32.52,32.70,32.04,32.19,41344800,32.19";
+          "2012-03-27,32.65,32.70,32.40,32.52,36274900,32.52";
+          "2012-03-26,32.19,32.61,32.15,32.59,36758300,32.59";
+          "2012-03-23,32.10,32.11,31.72,32.01,35912200,32.01";
+          "2012-03-22,31.81,32.09,31.79,32.00,31749500,32.00";
+          "2012-03-21,31.96,32.15,31.82,31.91,37928600,31.91";
+          "2012-03-20,32.10,32.15,31.74,31.99,41566800,31.99";
+          "2012-03-19,32.54,32.61,32.15,32.20,44789200,32.20";
+          "2012-03-16,32.91,32.95,32.50,32.60,65626400,32.60";
+          "2012-03-15,32.79,32.94,32.58,32.85,49068300,32.85";
+          "2012-03-14,32.53,32.88,32.49,32.77,41986900,32.77";
+          "2012-03-13,32.24,32.69,32.15,32.67,48951700,32.67";
+          "2012-03-12,31.97,32.20,31.82,32.04,34073600,32.04";
+          "2012-03-09,32.10,32.16,31.92,31.99,34628400,31.99";
+          "2012-03-08,32.04,32.21,31.90,32.01,36747400,32.01";
+          "2012-03-07,31.67,31.92,31.53,31.84,34340400,31.84";
+          "2012-03-06,31.54,31.98,31.49,31.56,51932900,31.56";
+          "2012-03-05,32.01,32.05,31.62,31.80,45240000,31.80";
+          "2012-03-02,32.31,32.44,32.00,32.08,47314200,32.08";
+          "2012-03-01,31.93,32.39,31.85,32.29,77344100,32.29";
+          "2012-02-29,31.89,32.00,31.61,31.74,59323600,31.74"; ]
+
+    // Feel free to add extra [<Koan>] members here to write
+    // tests for yourself along the way. You can also try 
+    // using the F# Interactive window to check your progress.
+
+    let column columnname data =
+        data
+        |> List.head
+        |> Array.findIndex (fun x -> x = columnname) 
+
+    //greatest variance between the opening and closing price
+    let GreatestVariance rawData =
+        let data = rawData |> List.map splitCommas
+        let opening = data |> column "Open" 
+        let closing = data |> column "Close" 
+        let datetime = data |> column "Date" 
+        data 
+        |> List.tail
+        |> List.maxBy (fun array -> abs (System.Double.Parse(array.[opening]) - System.Double.Parse(array.[closing])))
+        |> (fun x -> x.[datetime])
+
+    [<Koan>]
+    let YouGotTheAnswerCorrect() =
+        let result = GreatestVariance stockData
+        AssertEquality "2012-03-13" result