Let's practice when and where to use Arrays and Hashes, as well as how to interact with them when they are used in combination.

In this exercise we are going to explore the use of Arrays and Hashes in a bit of detail. We will be talking about Rainbows and different color combinations. Before doing this, you should first read up on the basics of RGB color codes

We use variables to store information that we want to access and/or change later, but when creating those variables it is important that we choose the right data type for our information. Right now we only know a handful of data types, but in the future we are going to learn about many, many more different types of data. Each has its own use and we should consider that when picking which we use.

For example, if we wanted to store some different colors as their RGB color codes, we could do something like:

red_hex = "#FF0000"
green_hex = "#00FF00"
blue_hex = "#0000FF"

Or maybe:

red_rgb = "rgb(255,0,0)"
green_rgb = "rgb(0,255,0)"
blue_rgb = "rgb(0,0,255)"

think But what are the limitations of this?

We are showing the representations of the colors, but what if we wanted to make a color calculator? (spoiler alert: That's what we are going to do.) How could we access and/or change the values separately? We can do it, but it'd require some extra code that's not as readable as it could be.

For example, perhaps:

red_val = red_hex[1..2]

This would isolate the "FF" in "#FF0000" but there's an easier way. Getting individual values out of the rgb codes would be even harder because you can't index the three values the same way you can with the hex values. (i.e. In Hex, the Red in RGB is always the first two characters after the #. In RBG, the Red is not always characters 4 through 6 like it is in red_rgb. For example, in green_rgb it's actually only character 4)

think: What would be a better data structure for storing values like this so that we can access each piece individually or the collection as a whole?

Did you read the title? Ok, yes, arrays would make this better.

red = [255,0,0]
green = [0,255,0]
blue = [0,0,255]

If we do this, then we are easily able to isolate the pieces of red and manipulate them separately.

For example:

puts "Red intensity of #{red} = #{red[0]}"
puts "Green intensity of #{red} = #{green[0]}"
puts "Blue intensity of #{red} = #{blue[0]}"

Interestingly (and also, mind-blowing weirdly to me), when you add RED + GREEN in the RGB Color Model, you get YELLOW. Yeah, not a weird brown color. Yellow. (I just learned something about additive vs subtractive colors.)

def mix_colors(color1,color2)
  mixed_color = []
  3.times do |i|
    mixed_color[i] = color1[i] + color2[i]
  end
  return mixed_color
end

puts mix_colors(red,green)

See, I didn't make it up. RED + GREEN = YELLOW

think: Ok, but what if we don't know that rgb(255,255,0) is yellow. What if we wanted to be able to look up what English color describes rgb(255,255,0). What type of structure could we use to make this easier?

I think you read the title again. Ok, let's use a hash, because a hash is a key/value pair that allows us to map a key to a value.

Perhaps we have something like:

color_lookup = {
  [255,0,0] => "red",
  [255,125,0] => "orange",
  [255,255,0] => "yellow",
  [125,255,0] => "spring green",
  [255,255,0] => "green",
  [0,255,125] => "turquoise",
  [0,255,255] => "cyan",
  [0,125,255] => "ocean",
  [0,0,255] => "blue",
  [125,0,255] => "violet",
  [255,0,255] => "magenta",
  [255,0,125] => "raspberry"
}

Then we could say:

new_color = mix_colors(red,green)
puts "#{color_lookup[red]} #{red} + #{color_lookup[green]} #{green} = #{color_lookup[new_color]} #{new_color}"

Success! If you run rainbows.rb you'll see that by using the code above, we can do some color calculations.

Result of rainbows.rb

red [255, 0, 0] + green [0, 255, 0] = yellow [255, 255, 0]

Play around with calling mix_colors on different arrays and see what you get.

puts color_lookup[mix_colors([0,125,0],[0,0,255])]

think: Why did we choose to use arrays where we used arrays and hashes where we used hashes? If you would have made a different data type choice, what and why would you have done differently?

Ok, so now let's start meshing together arrays and hashes and see what happens.

TODO #1 Let's create a rainbow of colors as an array of hashes, where each hash contains the name of the color (key) and the RGB values (value).

For example rainbow[0] would be a hash and have a key of

:red

and a value of

{
  r: 255,
  g: 0,
  b: 0
}

Again, this means you are creating an array of hashes, where each hash in the array has a symbol as its key and a hash as its value. That's a lot to digest.

Model your array of hashes after the following:

TODO #2 Use your rainbow array to print out each color name in sequence.

So your output could look like (or maybe something fancier):

red
orange
yellow
green
blue
indigo
violet

TODO (optional) Print the color name in the color it represents using the colorize gem or the rainbow gem.

Sample Solution

You're not done yet! Oh wait, I don't have time to finish this. So you get off easy for right now.

I was going to make you do something with this: