You can create an array by listing some items within square brackets ([]) and separating them with commas. Ruby's arrays can accomodate diverse object types.

Arrays can be concatenated or repeated just as strings can. See for yourself!

ary = [1, 2, "3"]
ary + ["foo", "bar"]

Output

ruby> ary = [1, 2, "3"]
   [1, 2, "3"]
ruby> ary + ["foo", "bar"]
   [1, 2, "3", "foo", "bar"]

ary = [1, 2, "3"]
ary * 2

Output

ruby> ary = [1, 2, "3"]
   [1, 2, "3"]
ruby> ary * 2
   [1, 2, "3", 1, 2, "3"]

We can use index numbers to refer to any part of a array. Negative indices mean offsets from the end of an array, rather than the beginning. The index of the last character is -1.

ary = [1, 2, "3"]
ary[0]
ary[0,2]
ary[0..1]
ary[-2]
ary[-2,2]
ary[-2..-1]

Output

ruby> ary = [1, 2, "3"]
   [1, 2, "3"]
ruby> ary[0]
   1
ruby> ary[0,2]
   [1, 2]

ruby> ary[0..1]
   [1, 2]
ruby> ary[-2]
   2
ruby> ary[-2,2]
   [2, "3"]

ruby> ary[-2..-1]
   [2, "3"]

Arrays can be converted to and from strings, using join and split respecitvely:

ary = [1, 2, "3"]
str = ary.join(":")
puts str.split(":")

Output

ruby> ary = [1, 2, "3"]
   [1, 2, "3"]
ruby> str = ary.join(":")
   "1:2:3"
ruby> puts str.split(":")
1
2
3
   nil
ruby> exit

We could use join to modify the preceeding example better so that each array item is printed, separated by spaces (without using eval.rb):

ary = [1, 2, "3"]
puts "ary[0]=#{ary[0]}"
puts "ary[0,2]=#{ary[0,2].join(" ")}"
puts "ary[0..1]=#{ary[0..1].join(" ")}"
puts "ary[-2]=#{ary[-2]}"
puts "ary[-2,2]=#{ary[-2,2].join(" ")}"
puts "ary[-2..-1]=#{ary[-2..-1].join(" ")}"

Output

ary[0]=1
ary[0,2]=1 2
ary[0..1]=1 2
ary[-2]=2
ary[-2,2]=2 3
ary[-2..-1]=2 3

Hashes

An associative array has elements that are accessed not by sequential index numbers, but by keys which can have any sort of value. Such an array is sometimes called a hash or dictionary; in the ruby world, we prefer the term hash. A hash can be constructed by quoting pairs of items within curly braces ({}). You use a key to find something in a hash, much as you use an index to find something in an array.

h = {1 => 2, "2" => "4"}
h[5] = 10  # appending an entry
h.delete 1
h[1]
h

Output

ruby> h = {1 => 2, "2" => "4"}
   {1=>2, "2"=>"4"}
ruby> h[5] = 10  # appending an entry
   10
ruby> h.delete 1
   2
ruby> h[1]
   nil
ruby> h
   {5=>10, "2"=>"4"}
ruby> exit

Here is a similar program (that is not run through eval.rb) that you can play with to understand Ruby arrays better:

h = {1 => 2, "2" => "4"}
puts "h[1] = #{h[1]}"
puts "h[\"2\"] = #{h["2"]}"
puts "h[5] = #{h[5]}"
h[5] = 10  # appending an entry
puts "after appending an entry:"
puts "h[5] = #{h[5]}"
h.delete 1
puts "Deleted entry with key 1"
puts "h[1] = #{h[1]}"
puts "h[\"2\"] = #{h["2"]}"
puts "h[5] = #{h[5]}"

Output

h[1] = 2
h["2"] = 4
h[5] = 
after appending an entry:
h[5] = 10
Deleted entry with key 1
h[1] = 
h["2"] = 4
h[5] = 10