[erlang-questions] escript cutting output

[Bob Gustafson]

Thanks much - dict seems to be the equivalent of the Ruby hash table.

I'm on a trip until Wednesday - don't know if I will have a chance to
work with your code until afterwards.

Bob G

On Sun, 2011-11-20 at 16:26 +0100, Jesper Louis Andersen wrote:
> On 2011-11-20 07:53, Bob Gustafson wrote: 
> > $ cat b_read.rb
> > #!/usr/env ruby
> > 
> > fin = File.open("buffer.out","r")
> > count = {}
> > fin.each_line do |line|
> >   line.each_char do |c|
> >     if count[c] == nil
> >        count[c] = 1
> >     else
> >        count[c] += 1
> >     end
> >   end
> > end
> 
> Not tested, but here is a general idea. Define a module and export the
> relevant function.
> 
> -module(foo).
> 
> -export([go/1]).
> 
> Now, go/1 will open the file in buffered mode so we get a little bit
> of read_ahead speedup. Opening the file as  a binary is even faster
> but for now, this will definitely do.
> 
> go(FN) ->
>     %% fin = File.open("buffer.out","r")
>     {ok, Fd} = file:open(FN, [read, read_ahead, raw]),
>     R = frequency_count(Fd),
>     file:close(Fd),
>     {ok, R}.
> 
> The way to count frequencies is to read in the first line, and keep a
> dictionary with us to update. We initialize the dictionary as the
> empty one.
> 
> frequency_count(IODev) ->
>     %% count = {}
>     frequency_count(IODev, file:read_line(IODev), dict:new()).
> 
> Two patterns. Either there is a line, in which case we process it, or
> there are no more lines, in which case we return the dictionary.
> 
> %% fin.each_line do |line|
> frequency_count(IODev, {ok, Line}, Dict) ->
>     frequency_count(IODev, file:read_line(IODev),
>                     update_line(Line, Dict));
> frequency_count(_IODev, eof, Dict) -> Dict.
> 
> Same game, either there is another character or there isn't. When we
> are done with the line, we return the dict. When there is a line, the
> scheme in the Ruby code can be handled by the function
> dict:update_counter/3, and by noticing we can process each character
> one at a time.
> 
> %%   line.each_char do |c|
> update_line([Char | Rest], Dict) ->
> %%     if count[c] == nil
> %%        count[c] = 1
> %%     else
> %%        count[c] += 1
> %%     end
>     NewDict = dict:update_counter(Char, 1, Dict),
>     update_line(Rest, NewDict);
> update_line([], Dict) -> Dict.
> 
> -- 
> Jesper Louis Andersen
>   Erlang Solutions, Copenhagen, DK
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