Change 'vector' and 'matrix' builder function in F# to take sequences instead of lists

@albertp007 wrote:

Hi all, the current 'vector' and 'matrix' functions in the F# extension modules take lists as input and create a DenseVector/DenseMatrix respectively. How about we change them to take sequences like so:

let inline vector (s: seq<'T>) = DenseVector.ofSeq s

and for matrix:

let inline matrix (s: seq<#seq<'T>>) = DenseMatrix.ofRowSeq s

F# takes sequence as anything that implements the IEnumerable interface, that includes lists, arrays, sequence expressions as well. So making the above changes will not affect existing functionality but then will open a lot more possibilities like the below:

It will still work for the existing case using list.

> open MathNet.Numerics.LinearAlgebra;;
> let v0 = vector [1.0; 2.0; 3.0];;

val v0 : Vector

It will even work for vector itself because vector also implements IEnumerable.

> let v1 = vector v0;;

val v1 : Vector

v1;;
val it : Vector = seq [1.0; 2.0; 3.0]

If you have an array of floats, it will also work:

> let a0 = [|1.0; 2.0; 3.0|];;

val a0 : float [] = [|1.0; 2.0; 3.0|]

> let v2 = vector a0;;

val v2 : Vector

> v2;;

val it : Vector = seq [1.0; 2.0; 3.0]

Using a sequence expression:

> seq { for i in [0.0..5.0] -> i * 2.0 } |> vector;;
val it : Vector = seq [0.0; 2.0; 4.0; 6.0; ...]

For matrix, the existing case using lists still works:

> matrix [[1.0; 2.0; 3.0]; [0.1; 0.2; 0.3]];;
val it : Matrix =
DenseMatrix 2x3-Double
1 2 3
0.1 0.2 0.3

{ColumnCount = 3;
 Item = ?;
 RowCount = 2;
 Storage = MathNet.Numerics.LinearAlgebra.Storage.DenseColumnMajorMatrixStorage`1[System.Double];
 Values = [|1.0; 0.1; 2.0; 0.2; 3.0; 0.3|];}

Or if you like you can do array of lists and it will work:

> matrix [| [1.0; 2.0; 3.0]; [0.1; 0.2; 0.3] |];;
val it : Matrix =
DenseMatrix 2x3-Double
1 2 3
0.1 0.2 0.3

{ColumnCount = 3;
 Item = ?;
 RowCount = 2;
 Storage = MathNet.Numerics.LinearAlgebra.Storage.DenseColumnMajorMatrixStorage`1[System.Double];
 Values = [|1.0; 0.1; 2.0; 0.2; 3.0; 0.3|];}

You can also use list of arrays:

> matrix [[|1.0; 2.0; 3.0|]; [|0.1; 0.2; 0.3|]];;
val it : Matrix =
DenseMatrix 2x3-Double
1 2 3
0.1 0.2 0.3

{ColumnCount = 3;
 Item = ?;
 RowCount = 2;
 Storage = MathNet.Numerics.LinearAlgebra.Storage.DenseColumnMajorMatrixStorage`1[System.Double];
 Values = [|1.0; 0.1; 2.0; 0.2; 3.0; 0.3|];}

And then you can also plug in a list of vectors and it will work too (because, again, vector implements IEnumerable)

> matrix [v2; v2];;
val it : Matrix =
DenseMatrix 2x3-Double
1 2 3
1 2 3

{ColumnCount = 3;
 Item = ?;
 RowCount = 2;
 Storage = MathNet.Numerics.LinearAlgebra.Storage.DenseColumnMajorMatrixStorage`1[System.Double];
 Values = [|1.0; 1.0; 2.0; 2.0; 3.0; 3.0|];}

The last case using a list/seq/array of vectors to create a matrix seem very natural to me and it will save us a lot of toList conversions.

Does anybody like this? Or there might be a reason why they only take lists to begin with, please feel free to share/comment

Cheers,
Albert

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