Re: [Caml-list] Create Array of floats from string

[Gabriel Scherer <gabriel.scherer@gmail.com>]

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> Can this Stream reading make use of the scanf to read floats (and other
words)?

Not really (although you can make do with Scanf.Scanning.from_function :
(unit -> char) -> Scanning.in_channel;
https://caml.inria.fr/pub/docs/manual-ocaml/libref/Scanf.Scanning.html ).

If counting the line number is important to you, it makes sense to keep
using input_line, instead of scanning " %f" directly on the channel (as
this may skip arbitrarily many newlines) but then you can still use it to
scan each line as a string:

  let line = input_line channel in
  let scanbuf = Scanf.Scanning.from_string line in
  incr line_number;
  Scanf.bscanf "%s@ " ignore;
  let vec = Array.init !dims (fun _ -> Scanf.bscanf scanbuf " %f" (fun x ->
x)) in
  ...

(the format "%s@c" means "scan a string until the character (c) excluded,
so "%s@ " consumes the first word.)

On Wed, Apr 26, 2017 at 10:05 AM, Jon Kleiser <jon.kleiser@ceres.no> wrote:

> Thanks a lot, Gabriel, for your idea about using the “word by word”
> method. This far I have used the Stream way of file reading:
>
> let line_stream_of_channel channel =
>   Stream.from
>     (fun _ -> try Some (input_line channel) with End_of_file -> None)
>
> Can this Stream reading make use of the scanf to read floats (and other
> words)? If not, I may leave the Stream way.
>
> I would also like to have access to the current number of lines received,
> to be able to report that so-and-so was found at line number x. This far I
> have not found out how count the lines while reading from a Stream.
>
> /Jon
>
>
> > On 26. Apr, 2017, at 15:41, Gabriel Scherer <gabriel.scherer@gmail.com>
> wrote:
> >
> > It looks like you read a line from an input channel and now want to
> split it on its spaces. It is also possible to read the input channel word
> by word in the first place, and for this the semantics of spaces in a scanf
> format is very useful: a single space ignores all whitespace. So
> >
> > let read_float () =
> >   Scanf.scanf " %f" (fun x -> x)
> >
> > will ignore any whitespace and then expect a floating-point number, read
> it and return it. (This reads from standard input, to read from arbitrary
> channels see Scanf.bscanf and the Scanf.Scanning module).
> >
> > On Wed, Apr 26, 2017 at 6:48 AM, Jon Kleiser <jon.kleiser@ceres.no>
> wrote:
> > Hi,
> >
> > I am quite new to OCaml, and I am looking for the most efficient way to
> make an Array of floats from string. My solution this far looks like this,
> where dims is a global variable specifying the size of the Arrays
> (typically 300):
> >
> > let make_vector vec_strings =
> >   let vec = Array.make !dims 0.0 in
> >   List.iteri (fun i str -> vec.(i) <- float_of_string str) vec_strings
> >
> > let process_line line =
> >   let parts = Str.split (Str.regexp " ") line in
> >   make_vector (List.tl parts)   (* skipping first element which is not a
> float *)
> >
> > /Jon
> >
> > --
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> >
>
>
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