Koan 15 (stock data): Wrong assertion

[maxild]

Hi,

I really like the project. So much better than a cheatsheet.

Using the F# Interactive (fsi) on

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"; ]

let parseLine (s:string) =
            s.Split [|','|]

let parseFloat s =
    System.Double.Parse(s, System.Globalization.CultureInfo.InvariantCulture)

// find the day with the greatest difference between the opening and closing prices.
let result =  stockData
              |> List.skip 1
              |> List.map parseLine
              |> List.map (fun arr -> (arr.[0], parseFloat arr.[1], parseFloat arr.[2]))
              |> List.map (fun (d, h, l) -> (d, h - l))   // [1]
              |> List.maxBy (snd >> abs)        
              |> fst   // [2]

By running until [1] in fsi

val result : (string * float) list =
  [("2012-03-30", -0.01); ("2012-03-29", -0.13); ("2012-03-28", -0.18);
   ("2012-03-27", -0.05); ("2012-03-26", -0.42); ("2012-03-23", -0.01);
   ("2012-03-22", -0.28); ("2012-03-21", -0.19); ("2012-03-20", -0.05);
   ("2012-03-19", -0.07); ("2012-03-16", -0.04); ("2012-03-15", -0.15);
   ("2012-03-14", -0.35); ("2012-03-13", -0.45); ("2012-03-12", -0.23);
   ("2012-03-09", -0.06); ("2012-03-08", -0.17); ("2012-03-07", -0.25);
   ("2012-03-06", -0.44); ("2012-03-05", -0.04); ("2012-03-02", -0.13);
   ("2012-03-01", -0.46); ("2012-02-29", -0.11)]

And running all the way to [2] in fsi

val result : string = "2012-03-01"

Therefore the assertion should be

AssertEquality "2012-03-01" result

and not this

I kind of find it hard to believe that I am the first to report this, so maybe I am doing something wrong, Anyway go figure. And thanks for sharing this great intro to F#.

[maxild]

I kind of find it hard to believe that I am the first to report this, so maybe I am doing something wrong, Anyway go figure. And thanks for sharing this great intro to F#.

Nevermind: Opening and Closing prices...column 1 and 4, I should learn to read

[ChrisMarinos]

It’s all good- making mistakes is part of the learning process!