Re: [Caml-list] laconical input from a file for arrays and/or matrices

["Issac Trotts" <ijtrotts@ucdavis.edu>]

On Mon, Feb 02, 2004 at 11:42:18AM +0100, Khamenia, Valery wrote:
> Hi OCaMLers,
> 
>   here goes my usual way to input ASCII matrices from file in C++:
> 
> //  -------  start of fragment -----------
> #include <iostream>
> #include <vector>
> using namespace std;
> 
> void input_matrix(vector<vector<double > >&vec) {
>   int m, n;
>   cin >> m;
>   cin >> n;
>   vec.resize (m);
>   for( int i = 0; i<m; i++)
>     vec[i].resize(n);
>   for( int i = 0; i<m; i++)
>     for( int j = 0; j<n; j++) 
>       cin >> vec[i][j]; 
> }
> //  -------- end of fragment -------------
> 
> then for matrix :
> 
>   3
>   3
>   1 2 3 
>   4 5 6
>   7 8 9
> 
> stored in ASCII text file mymatrix.dat
> 
> i just run my program:
> 
>  % myprogram < mymatrix.dat
> 
> and it is done.
> 
> Thus, the few lines of code and i can apply all math I need. 

Here's a way to do it with camlp4.  You get OCaml-style comments 
for free from Genlex this way:

#load "camlp4o.cma";; 
open Genlex;;

let input_matrix channel = 
  let read_number = parser
      [< 'Int i >] -> float i
    | [< 'Float f >] -> f in
  let rec read_nums n = 
    if n = 0 
      then parser [< >] -> [] 
      else parser [< head=read_number; tail=read_nums (n-1) >] -> head::tail in 
  let rec read_matrix_data m n = 
    if m = 0 
      then parser [< >] -> []
      else parser
        [< row = read_nums n; rest = read_matrix_data (m-1) n >] -> 
          (Array.of_list row) :: rest in
  let read_matrix = parser 
    [< 'Int m; 'Int n; rest >] ->
      let rows = read_matrix_data m n rest in
      Array.of_list rows in
  let charstream = Stream.of_channel channel in
  let lexer = Genlex.make_lexer [] charstream in
  read_matrix lexer;;

input_matrix stdin;;

-- 
Issac Trotts
http://redwood.ucdavis.edu/~issac

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