问题
In Matlab we can write the following code to shuffle a matrix:
data = data(:, randperm(size(data,2)));
there is what I write with Math.NET:
let csvfile = @"../UFLDL-tutorial-F#/housing.csv"
let housingAsLines =
File.ReadAllLines(csvfile)
|> Array.map (fun t -> t.Split(',')
|> Array.map (fun t -> float t))
let housingAsMatrix= DenseMatrix.OfRowArrays housingAsLines
let housingAsMatrixT = housingAsMatrix.Transpose()
let v1 = DenseVector.Create(housingAsMatrixT.ColumnCount,1.0)
housingAsMatrixT.InsertRow(0,v1)
// How to shuffle a "DenseMatrix" in F#
To simulate matrix operation in Matlab, using the F# slice syntax and zero-based indexing. However, it doesn't work.
housingAsMatrixT.[*,0]
And I got the error message in vscode.
The field, constructor or member 'GetSlice' is not defined
回答1:
You actually have two questions, 1) how to slice Matrices ala matlab and 2) how to shuffle the columns of a matrix.
For 1) actually Issue 277 you linked in the comment does indeed provide the solution. However you might be using an old version or you might not be referencing the F#
extensions correctly:
#r @"..\packages\MathNet.Numerics.3.13.1\lib\net40\MathNet.Numerics.dll"
#r @"..\packages\MathNet.Numerics.FSharp.3.13.1\lib\net40\MathNet.Numerics.FSharp.dll"
open MathNet.Numerics
open MathNet.Numerics.LinearAlgebra
open MathNet.Numerics.Distributions
open System
//let m = DenseMatrix.randomStandard<float> 5 5
let m = DenseMatrix.random<float> 5 5 (ContinuousUniform(0., 1.))
let m' = m.[*,0]
m'
//val it : Vector<float> =
//seq [0.4710989485; 0.2220238937; 0.566367266; 0.2356496324; ...]
This extracts the first column of the matrix.
Now for 2), assuming you need to shuffle the matrix or the arrays containing a matrix you can use some of the approaches below. There might be a more elegant method within mathnet.numerics
.
To permute the vector above: m'.SelectPermutation()
or SelectPermutationInplace
for arrays. There are other convenience function like .Column(idx)
,.EnumerateColumnsIndexed()
or EnumerateColumns()
, etc.
So m'.SelectPermutation()
will shuffle the elements of m'. Or to shuffle the columns (which your matlab function does):
let idx = Combinatorics.GeneratePermutation 5
idx
//val it : int [] = [|2; 0; 1; 4; 3|]
let m2 = idx |> Seq.map (fun i -> m.Column(i)) |> DenseMatrix.ofColumnSeq
m2.Column(1) = m.Column(0)
//val it : bool = true
Since the first column of the original matrix moved to the second column of the new matrix, the two should be equal.
回答2:
With Neural Networks I had to shuffle an array of Matrices and used the following code. Note the base data structure is an array ([]) and each item in the array is a Matrix. This is not shuffling a matrix, but an array. It should give you some idea of how to proceed for your problem.
type Random() =
static member Shuffle (a : 'a[]) =
let rand = new System.Random()
let swap (a: _[]) x y =
let tmp = a.[x]
a.[x] <- a.[y]
a.[y] <- tmp
Array.iteri (fun i _ -> swap a i (rand.Next(i, Array.length a))) a
and called it like
Random.Shuffle trainingData
Addendum
Here is the code to convert a byte[]
to a DenseMatrix
of double
let byteArrayToMatrix (bytes : byte[]) : Matrix<double> =
let (x : Vector<byte>) = Vector<byte>.Build.DenseOfArray bytes
let (y : Vector<double>) = x.Map(fun x -> double x)
let (z : Matrix<double>) = Matrix<double>.Build.DenseOfRowVectors y
z
回答3:
@GuyCoder and @s952163, thanks for your help. I implemented a quick-and-dirty version. It is not good enough but it works.
Please feel free to comment. Thank you.
#load "../packages/FsLab.1.0.2/FsLab.fsx"
open System
open System.IO
open MathNet.Numerics.LinearAlgebra.Double
open MathNet.Numerics
open MathNet.Numerics.LinearAlgebra
open MathNet.Numerics.Distributions
// implementation of the Fisher-Yates shuffle by Mathias
// http://www.clear-lines.com/blog/post/Optimizing-some-old-F-code.aspx
let swap fst snd i =
if i = fst then snd else
if i = snd then fst else
i
let shuffle items (rng: Random) =
let rec shuffleTo items upTo =
match upTo with
| 0 -> items
| _ ->
let fst = rng.Next(upTo)
let shuffled = List.permute (swap fst (upTo - 1)) items
shuffleTo shuffled (upTo - 1)
let length = List.length items
shuffleTo items length
let csvfile = @"/eUSB/sync/fsharp/UFLDL-tutorial-F#/housing.csv"
let housingAsLines =
File.ReadAllLines(csvfile)
|> Array.map (fun t -> t.Split(',')
|> Array.map (fun t -> float t))
let housingAsMatrix= DenseMatrix.OfRowArrays housingAsLines
let housingAsMatrixTmp = housingAsMatrix.Transpose()
let v1 = DenseVector.Create(housingAsMatrixTmp.ColumnCount,1.0)
let housingAsMatrixT = housingAsMatrixTmp.InsertRow(0,v1)
let m = housingAsMatrixT.RowCount - 1
let listOfArray = [0..m]
let random = new Random()
let shuffled = shuffle listOfArray random
let z = [for i in shuffled -> (housingAsMatrixT.[i, *])]
let final = DenseMatrix.OfRowVectors z
来源:https://stackoverflow.com/questions/40466407/how-to-shuffle-a-densematrix-in-f