Merge pull request #406 from zyzhu/issue-364

Avoid iterating seq multiple times in Frame.ofRecords

src/Deedle/FrameUtils.fs

@@ -215,10 +215,11 @@ module internal Reflection =
       [| for _, (input, body) in convertors ->
            let cast = Expression.Convert(body, typeof<IVector>)
            Expression.Lambda<Func<seq<'T>, IVector>>(cast, input).Compile() |]
+    let data = data |> Array.ofSeq
     let frameData =
       [| for convFunc in convertors -> convFunc.Invoke(data) |]
       |> vectorBuilder.Create
-    Frame<int, string>(Index.ofKeys [0 .. (Seq.length data) - 1], colIndex, frameData, IndexBuilder.Instance, VectorBuilder.Instance)
+    Frame<int, string>(Index.ofKeys [0 .. data.Length - 1], colIndex, frameData, IndexBuilder.Instance, VectorBuilder.Instance)
 
   /// Helper that makes it possible to call convertRecordSequence on untyped enumerable
   type ConvertRecordHelper =

tests/Deedle.Tests/Frame.fs

@@ -353,6 +353,18 @@ let ``Can read simple sequence of records using a specified column as index`` ()
   set df.ColumnKeys |> shouldEqual (set ["Volume"; "Price"])
   df.RowKeys |> Seq.head |> shouldEqual rows.[0].Date
 
+[<Test>]  
+let ``Can read simple sequence of records deterministically `` () =
+  let mutable n = 0
+  let values = 
+    seq { 
+      yield n, n
+      n <- n + 1
+      yield n, n
+      n <- n + 1 }
+  let expected = [|0, 0; 1, 1|] |> Frame.ofRecords
+  values |> Frame.ofRecords |> shouldEqual expected
+
 [<Test>]  
 let ``Can expand properties of a simple record sequence`` () =
   let df = frame [ "MSFT" => Series.ofValues (typedRows ()) ]