Hashes

Hash it out

So we've looked at arrays already, but arrays have a weird step-brother called hashes. Let's look at an example:

font_options = { :size => 12, :font_family => "Times New Roman" }
font_options.length

With hashes, we store collections of objects, just like we did with Arrays earlier. Unlike arrays, which stored objects in order (like color_ary[0], color_ary[1], etc.), Hashes store objects as values stored at a named key. In our hash above, :size and :font_family are keys, and 12 and "Times New Roman" are values stored at the respective keys. Keys are usually symbols, which start with a colon (:).

The values are specified with something we call the hashrocket that looks like =>. There is also a newer syntax as of Ruby version 1.9 that looks like size: 12, font_family: "Times New Roman" but there are certain situations where that syntax can make methods confusing, especially when we get to Rails, so let's stick with the hashrocket syntax, at least for now.

Go ahead and make a hash called abbr that stores 5 abbreviations, with the abbreviation themselves set as the keys and the phrase being abbreviated set as the values (e.g. "NSA" : "National Security Agency").

We can also loop through hashes, just like we did with Arrays earlier:

font_options.each do |key, value|
  puts key.to_s + ":"
  puts value
end

Notice that, unlike arrays, we need to pass an argument for both the key and the value when looping through a hash.

Exercise 6

Go ahead and loop through your abbr hash and print out the keys and values in an attractive way.