Forum: Ruby Another Newb asks questions.

Announcement (2017-05-07): www.ruby-forum.com is now read-only since I unfortunately do not have the time to support and maintain the forum any more. Please see rubyonrails.org/community and ruby-lang.org/en/community for other Rails- und Ruby-related community platforms.
Joseph D. (Guest)
on 2005-12-30 21:54
Ok, recently started "trying" to learn this wonderful language, but am
experiencing major problems with a section of code that I think "should"
work.. and my brain is so convinced that I did it correctly that I can't
see some obvious error.  Ive isolated the problem to this single section
of code.. what do you all think?


#This section reads data files and saves odd lines as the key, even
lines as the value for a hash.

if Dir["/Program Files/.../data/"].last != nil
        script_data_dir = "/Program Files/.../data/"
end
build_hash = Proc.new do |type|
		hash.new = type_hash
		file.open("#{script_data_dir}type.dat", "r") { |file|
			data = file.readlines
			data.delete_if { |line| line.chomp.empty? }
				until data.empty?
				$type_hash[data.shift.chomp] = data.shift.chomp
				end
		}
end
build_hash.call(test)
end

Thanks for any help in advance..

Joseph
Wilson B. (Guest)
on 2005-12-31 00:37
(Received via mailing list)
On 12/30/05, Joseph D. <removed_email_address@domain.invalid> wrote:
> if Dir["/Program Files/.../data/"].last != nil
>                 }
> end
> build_hash.call(test)
> end
>

This solution uses the 'enumerator' module, included in the standard
library.

require 'enumerator'
Dir.chdir(script_data_dir)
type_hash = Hash.new
File.open('type.dat','r') do |file|
  file.each_slice(2) do |odd, even|
    type_hash[odd.chomp] = even.chomp
  end
end

each_slice(2) is taking each pair of lines in the file, and passing
them to the block.  So, [line1, line2], then [line3, line4], etc, etc.
You should probably also have a check in there to make sure the file
has an even number of lines.

You can also use File.exists?() to check for the presence of a
directory.
abort "Oh no!" unless File.exists?("C:/Program
Files/something/data_dir")
Joseph D. (Guest)
on 2005-12-31 00:56
Wilson B. wrote:

> This solution uses the 'enumerator' module, included in the standard
> library.
>

Very good solution.  Ill look into it ans see how it works.  Thanks.
Wilson B. (Guest)
on 2005-12-31 01:10
(Received via mailing list)
On 12/30/05, Joseph D. <removed_email_address@domain.invalid> wrote:
> Wilson B. wrote:
>
> > This solution uses the 'enumerator' module, included in the standard
> > library.
> >
>
> Very good solution.  Ill look into it ans see how it works.  Thanks.
>
Here's another, much uglier solution, that doesn't rely on Enumerator.
There's probably a better way, but hey, you get what you pay for. :)

Dir.chdir(script_data_dir)
type_hash = Hash.new
File.open('type.dat','r') do |file|
  odd = [] ; even = []
  file.each do |line|
    if file.lineno % 2 == 1 then odd << line.chomp
    else even << line.chomp end
  end
  odd.each_with_index { |line, i| type_hash[line] = even[i]}
end
Joseph D. (Guest)
on 2005-12-31 03:02
Wilson B. wrote:
>     if file.lineno % 2 == 1 then

I hope youll forgive, but I seem to be at a loss for exactly what/how
this is doing..?

Any clarification?

Yeah this is my first language, first project, first week; so label me
silly.
Christer N. (Guest)
on 2005-12-31 03:44
Joseph D. wrote:
> Wilson B. wrote:
>>     if file.lineno % 2 == 1 then
>
> I hope youll forgive, but I seem to be at a loss for exactly what/how
> this is doing..?
>
> Any clarification?
>
> Yeah this is my first language, first project, first week; so label me
> silly.

It seems to check if the line number is odd. % is the modulo operator.

class Integer
  def odd?
    self % 2 == 1
  end
end

 ... if file.lineno.odd? then ...

we have all been in your situation :-)

Christer
Matthew S. (Guest)
on 2005-12-31 03:53
(Received via mailing list)
On Dec 31, 2005, at 1:02, Joseph D. wrote:

> Wilson B. wrote:
>>     if file.lineno % 2 == 1 then
>
> I hope youll forgive, but I seem to be at a loss for exactly what/how
> this is doing..?
>
> Any clarification?
>
> Yeah this is my first language, first project, first week; so label me
> silly.

% is the modulo operator.  It gives the remainder of integer division:
x / y = a (rem b)
y * a + b = x

Concrete example:
17 / 3 = 5 (rem 2)
5 * 3 + 2 = 17

Modulo returns 0 if the numerator is evenly divisible by the
denominator, so modulo 2 is a good way to check if a number is even.

m.s.
Joseph D. (Guest)
on 2005-12-31 04:28
Great answers guys!  Thanks for the help.. surprisingly a part of what
was throwing me off was not having food in the tummy apparently, as when
that problem was fixed I immediately realized part of my problem was not
knowing what "file.lineno" was.. and all I can say is "duh".  Makes alot
of sense now. and good trick with the % very crafty.
Joseph D. (Guest)
on 2005-12-31 06:06
Thanks again all.. so that you know your efforts wern't in vain I think
I learned a thing or two.  The rough code (still needing debugging about
as much as I need sleep) is below.  I have a high level of confidence
that I will find the typo or missing end to make it work when I wake up
in the morning.

require 'enumerator'
if Dir["#{$script_dir}data/"].last != nil
        script_data_dir = "#{$script_dir}data/"
end
build_hash = Proc.new do |type|
	type_hash = Hash.new
	file.open("#{script_data_dir}#{type}.dat", "r") do |file|
		file.each_slice(2) do |key, value|
			type_hash[key.chomp] = value.chomp
		end
	end
	$type_hash = type_hash
end
data_files=Dir["#{script_data_dir}*.dat"]
data_files.each do |name_of_file|
build_hash.call(file.basename(name_of_file, '*.*'))
end

VR,

Joseph
Daniel H. (Guest)
on 2005-12-31 07:26
(Received via mailing list)
Joseph D. wrote:
> if Dir["#{$script_dir}data/"].last != nil
> end
> Posted via http://www.ruby-forum.com/.
I see two typos --
1) file.open should be File.open ( actually, you can leave off File
too, so it is just open(..). See Kernel#open ).
2) file. basename should be File.basename

Slight style suggestions --
* The first conditional statement may be rewrote as:
   script_data_dir = "#{$script_dir}data/" unless Dir["#{$script_dir}
data/"].last.nil?
* {} is equivalent to Hash.new
* Use { |x| ... } block syntax when the block has only one simple
statement (the each_slice part)

-- Daniel
Robert K. (Guest)
on 2005-12-31 15:30
(Received via mailing list)
Daniel H. <removed_email_address@domain.invalid> wrote:
>> require 'enumerator'
>> $type_hash = type_hash
>> end
>> data_files=Dir["#{script_data_dir}*.dat"]

If I'm not mistaken there's a path separator missing.  You better use

data_files=Dir[File.join(script_data_dir, "*.dat")]

>> data_files.each do |name_of_file|
>> build_hash.call(file.basename(name_of_file, '*.*'))

What do you use the second parameter for?  The only reasonable value
here
seems to be '*.dat'.  Also you're trying to remove the suffix ".dat" and
reappend it again.  Seems a bit strange to me.

> 1) file.open should be File.open ( actually, you can leave off File
> too, so it is just open(..). See Kernel#open ).
> 2) file. basename should be File.basename

Also it's unnecessary since Dir[] always returns basenames *only*.

> Slight style suggestions --
> * The first conditional statement may be rewrote as:
>   script_data_dir = "#{$script_dir}data/" unless Dir["#{$script_dir}
> data/"].last.nil?

Even better would be to use File.directory? to test for presence of this
directory.  And it would be even better if the absence of the directory
would be handled properly.  As far as I can see at the moment
script_data_dir simply remains unset and thus the current working
directory
is used.

> * {} is equivalent to Hash.new
> * Use { |x| ... } block syntax when the block has only one simple
> statement (the each_slice part)

Don't use blocks or procs unless you need them (i.e. want to encapsulate
a
piece of code and refer it from a variable).

Don't assign a global variable as a side effect from your proc / method
if
you also return it.  There's especially the problem of your code that
you
only get the last hash because all others are lost (the global is
overwritten all the time).

Here's what I'd probably do:

require 'enumerator'

def build_hash(file)
  h = {}
  File.open(file, "r") do |io|
    io.each_slice(2) {|k,v| h[k.chomp]=v.chomp}
  end
  h
end

def build_hashes(dir='.')
  h = {}
  Dir[ File.join( dir, "*.dat") ].each do |file|
    h[ File.basename( file, ".dat" ) ] = build_hash( File.join(dir,
file) )
  end
  h
end

This builds a hash of hashes.  Dunno whether that's what you want.

HTH

    robert
Joseph D. (Guest)
on 2005-12-31 17:30
Daniel H. wrote:

> Slight style suggestions --
> * The first conditional statement may be rewrote as:
>    script_data_dir = "#{$script_dir}data/" unless Dir["#{$script_dir}
> data/"].last.nil?
> * {} is equivalent to Hash.new
> * Use { |x| ... } block syntax when the block has only one simple
> statement (the each_slice part)

Actually the first conditional will have elsifs once I get the code
working, hence the reason for writing it that way.  I intend to make it
viable for unix platform for the same program aswell, in which case I
will have to look elsewhere for the appropriate directory :(

Thanks,

Joseph
Joseph D. (Guest)
on 2005-12-31 17:42
Robert K. wrote:
> Daniel H. <removed_email_address@domain.invalid> wrote:
>>> require 'enumerator'
>>> $type_hash = type_hash
>>> end
>>> data_files=Dir["#{script_data_dir}*.dat"]
>
> If I'm not mistaken there's a path separator missing.  You better use
>
> data_files=Dir[File.join(script_data_dir, "*.dat")]
>

> What do you use the second parameter for?  The only reasonable value
> here
> seems to be '*.dat'.  Also you're trying to remove the suffix ".dat" and
> reappend it again.  Seems a bit strange to me.
>

Yeah I was being silly there. I actually intended to remove the
extension from the filename, thanks for the correction.

>> 1) file.open should be File.open ( actually, you can leave off File
>> too, so it is just open(..). See Kernel#open ).
>> 2) file. basename should be File.basename
>
> Also it's unnecessary since Dir[] always returns basenames *only*.
>

Thank you both.  seems that I was misunderstanding how Dir[] worked
exactly.  Ill play with that some more.


>> * {} is equivalent to Hash.new
>> * Use { |x| ... } block syntax when the block has only one simple
>> statement (the each_slice part)
>
> Don't use blocks or procs unless you need them (i.e. want to encapsulate
> a
> piece of code and refer it from a variable).
>

I am not exactly sure how you mean by this but I had thought I was doin
it with
   "build_hash.call(File.basename(name_of_file))"

> Don't assign a global variable as a side effect from your proc / method
> if
> you also return it.  There's especially the problem of your code that
> you
> only get the last hash because all others are lost (the global is
> overwritten all the time).
>

build_hash = Proc.new do |type|
	type_hash = Hash.new
...
	$type_hash = type_hash

What I had thought this would be doing is to take its input (aka.
Test1.dat or Test2.dat) and make Test1_hash, or Test2_hash and then
convert those to $Test1_hash or $Test2_hash for use elsewhere.  am I
experiencing a gross concept error here?
This topic is locked and can not be replied to.