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Array2 -> array of array conversion
f#

Hi, I'd like to convert a Array2 into a array array : 

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let of_array2 (mat) = 
let make_vec i = Array.create i 0. in 
let output = Array.create (Array2.length1 mat) (make_vec (Array2.length2 mat))
Array2.iteri (fun i j v -> output.(i).(j) <- v) mat
output

Now for instance, when converting a diag matrix (see code below) 

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let diag n = 
 let res = Array2.create n n 0.0
 for i= 0 to (n-1) do
    res.(i,i) <- 1.0
 res

Then (diag 3) |> of_array2 gives :

[|[|0.0; 0.0; 1.0|]; [|0.0; 0.0; 1.0|]; [|0.0; 0.0; 1.0|]|]

Where am I wrong ?

Thanks in advance

Julien

.

Your call to Array.create is placing the same physical vector in each column of the array - this matters when you are using mutation to initialize. Generally use Array.init and Array2.init to avoid this kind of aliasing. Try this:

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#light

let of_array2 (mat:float[,]) = 
    Array.init (Array2.length1 mat) (fun i -> 
        Array.init (Array2.length2 mat) (fun j -> 
           mat.[i,j]))

let diag n = 
  let res = Array2.zero_create n n 
  for i= 0 to (n-1) do
    res.[i,i] <- 1.0
  res


diag 3 |> of_array2
By on 11/7/2006 5:16 PM ()

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