Hash Expressions

[+ dbchest 160]

i don't fully understand the potential of hash arrays. i understand they act as a sort of road map for assigning values to symbols, etc. i would like to walk through some examples to get a better idea of how hash arrays work. below is a practical example of a system i am developing. i would appreciate if someone could help me understand how to pull the desired data:

  #--------------------------------------------------------------------------
  # * Constants (Graphics and Data Assignment)
  #--------------------------------------------------------------------------
  NOTESET = 'Noteset' # filename for graphics
  DATA    = {:DOWN  => ['Audio\SE\Cursor2', 0,  3],
             :LEFT  => ['Audio\SE\Cursor2', 1,  2],
             :RIGHT => ['Audio\SE\Cursor2', 2,  1],
             :UP    => ['Audio\SE\Cursor2', 3,  0],
             :A     => ['Audio\SE\Cursor2', 4,  2],
             :C     => ['Audio\SE\Cursor2', 6,  0]}
  #--------------------------------------------------------------------------
  # * Constants (Settings for Playback)
  #--------------------------------------------------------------------------

where:

[audio filename, index within spritesheet, line number for display]

 

now for the practical example:

  #--------------------------------------------------------------------------
  # * Draw All Notes
  #--------------------------------------------------------------------------
  def draw_all_notes
    @composition.each_index do |i|
      draw_note(WHAT CAN I PUT HERE?)
    end
  end
  #--------------------------------------------------------------------------
  # * Draw Note
  #--------------------------------------------------------------------------
  def draw_note(index, x, y)
    bitmap = Cache.system(NOTESET)
    rect = Rect.new(index % 6 * 24, index / 6 * 24, 24, 24)
    contents.blt(x, y, bitmap, rect)
  end

when defining my arguments, how can i pull the data from my hash array? i need to pull the spritesheet index and the line number.

[Tsukihime 1,487]

Well to work with a hash, you use keys and assign values to the keys.

 

# init hash
your_hash = {}

# assign something to a key
your_hash[:name] = "Hime"

# Access the value of the key
p your_hash[:name]

It's just a way to store your data.

 

I'm not sure what you actually want to know.

Edited October 10, 2013 by Tsukihime

[+ dbchest 160]

the console and you are life savers. don't lock this thread yet. i have a feeling i will have more questions about this, but i have a basic understanding.

Edited October 10, 2013 by dbchest

[Riff 62]

To put it roughly it's just like an array but instead of numeric index you can have whatever you want for an index.

[+ dbchest 160]

yea, turns out the main problem i experienced was using the proper method call for evaluating each element of my array with a block.

 

when working with symbols, you need the index processed as is so it reads the symbol. <= each do

when working with integers, you need the index processed as an integer so it can pull the index. <= each_index

when using hash arrays, you assign values to symbols, so naturally you will need a way to reference both types of data when evaluating a block. <= each_with_index

 

i kept using each do and each_index. i kept getting errors until i remembered about each_with_index and referenced both forms of my data for my block.

Edited October 11, 2013 by dbchest

[Xypher 176]

you can use each, each_key, each_value, each_pair for hashes too.

[+ dbchest 160]

very nice, that makes much more sense, haha.

[Riff 62]

For hashes you can go with

@hash.each{ |key, value|
  my stuff here}

I don't know if you can use #each (the simplest one) with only one 'block argument' though (key or value), never tested it but you have #each_key and #each_value for that matter.

Edited October 11, 2013 by Riff

[regendo 204]

According to ruby-doc, your options are:

hash.each {|key, value| do_stuff }
hash.each_pair {|key, value| do_stuff } # apparently the same
hash.each_key {|key| do_stuff } # keys only
hash.each_value {|value| do_stuff } # values only

http://www.ruby-doc.org/core-1.9.2/Hash.html#method-i-each

[+ dbchest 160]

yeah, i didn't take a real good look at the hash class. that was my bad. i spent a minute going over the methods listed, then i also checked ruby-doc (regendo provided me the link in the past) and now i'm up and running with hashes. i won't say i entirely understand how to reference values from them, because i still have to guess, test, and revise occasionally to grab the info i want, but that's a short price to pay.

 

thanks everyone.

[regendo 204]

I think it might help to simply think of hashes as arrays. Only that instead of putting a value in element #5, you put it in element "key" or element :blade.

[Tsukihime 1,487]

yea, turns out the main problem i experienced was using the proper method call for evaluating each element of my array with a block.

 

when working with symbols, you need the index processed as is so it reads the symbol. <= each do

when working with integers, you need the index processed as an integer so it can pull the index. <= each_index

when using hash arrays, you assign values to symbols, so naturally you will need a way to reference both types of data when evaluating a block. <= each_with_index

 

i kept using each do and each_index. i kept getting errors until i remembered about each_with_index and referenced both forms of my data for my block.

That doesn't really make sense to me.

 

each_with_index is the same as each except you have the index of the current element

 

[2,3,4].each_with_index do |num, i|
  p [num, i]
end

Results in

 

[2, 0]
[3, 1]
[4, 2]

[+ dbchest 160]

you're exactly right regendo.

 

tsukihime:

i'm developing my own version of a script that allows the player to perform instrumentals. the way i worded things above sounded bad because it comes off like i'm implying that those methods work the way i described above in general, but we know that's not true. in reality, i wanted to imply that in order to get the icons to draw on the screen properly (for my script alone), i needed to be able to reference both pieces of information.

 

when writing the definition to draw the icons, i repeatedly tried using each and each_index. i didn't take into account that those methods only reference one of the two pieces of information from the array's elements, and at the time i wrote that post i guess i didn't fully understand what each, each_index, and each_with_index actually referenced.

 

i believe this is how those methods work.

ray = [this, is, right] << if this is my array...
ray.each do |element|
 p element
end

ray.each_index do |index|
 p index
end

ray.each_with_index do |element, index|
 p element
 p index
end

will result in (respectively):

this
is
right

0
1
2

[this, 0]
[is, 1]
[right, 2]

correct me if i'm wrong?

Edited October 12, 2013 by dbchest

[Xypher 176]

http://codepad.org/ovuAA2mK

[+ dbchest 160]

Lol, thanks.