Sams Teach Yourself Ruby in 21 Days

Hashes

Array elements are referred to by numeric indices. A more general approach would be to allow any kind of object, not just a number, to refer to an array element. A hash, sometimes also called a dictionary or an associative array, has this ability.

h = Hash.new
h["Alabama"] = "humid"
h["Alaska"]  = "frigid"
h["Colorado"]  = "rocky"
h["Wisconsin"] = "cheesy"

# If you prefer, the above can also be written this way:
# h = {"Alabama"=>"humid",  "Alaska"=>"frigid",
#  "Colorado"=>"rocky", "Wisconsin"=>"cheesy"}

h.size  #–> 4
h["Alaska"]    #–> "frigid"
h["Missouri"]  #–> nil

What a hash gives you is essentially a two-column table with keys in one column and values in the other. Give the hash a key, and it tells you the associated value. If you look ...