Why you need to know Array & Hash?

Most of programming languages need to handle data structure.

For example, Ruby can put many order into Array(we also say it’s a kind of container), then it can use some method to calculate and handle data.

Ruby’s arrays and hashes are indexed collections. Both store collections of objects, accessible using a key. With arrays, the key is an integer, whereas hashes support any object as a key. Both arrays and hashes grow as needed to hold new elements.

Table of contents

1. Array
2. Hash

Array

1. A new array can be created by using the literal constructor []. Arrays can contain different types of objects

     irb(main):001:0> name = ["foo", "bar", "baz", "qux"]
     => ["foo", "bar", "baz", "qux"]
   

   

2. Access elements.

   The first element index is 0, other words name[1] is the SECOND element

     irb(main):001:0> name[0]
     => "foo"
     irb(main):002:0> name[1]
     => "bar"
     irb(main):001:0> name[2]
     => "baz"
     irb(main):001:0> name[3]
     => "qux"
     irb(main):001:0> name[4]
     => nil
   

3. Print data by access array element

     irb(main):001:0> print "The first element is ", name[0], "! \n"
     The first element is foo!
     => nil
   

4. Assign data into element

     irb(main):001:0> name = ["foo", "bar", "baz", "qux"]
     => ["foo", "bar", "baz", "qux"]
     irb(main):002:0> name[0] = "quux"
     => "quux"
     irb(main):003:0> name
     => ["quux", "bar", "baz", "qux"]
   

5. Ruby will auto adjust array size.

     irb(main):001:0> name = ["foo", "bar", "baz", "qux"]
     => ["foo", "bar", "baz", "qux"]
     irb(main):002:0> name[4] = "quux"
     => "quux"
     irb(main):003:0> name
     => ["foo", "bar", "baz", "qux", "quux"]
   

6. Array can assign every kinds of type object.

     irb(main):009:0> numbers = [1, 2, 3, 4, 5]
     => [1, 2, 3, 4, 5]
     irb(main):010:0> mixed = [1, 'foo', 2, 'bar', 3]
     => [1, "foo", 2, "bar", 3]
   

7. Array has a method size will return how many elements in this array.

     irb(main):001:0> name = ["foo", "bar", "baz", "qux"]
     => ["foo", "bar", "baz", "qux"]
     irb(main):002:0> name.size
     => 4
   

8. Array iterate by .each.

     irb(main):001:0> names = ["foo", "bar", "baz", "qux"]
     => ["foo", "bar", "baz", "qux"]
     irb(main):002:0> names.each do |name|
     irb(main):003:1* puts name
     irb(main):004:1> end
     foo                              -> from puts name
     bar                              -> from puts name
     baz                              -> from puts name
     qux                              -> from puts name
     => ["foo", "bar", "baz", "qux"]  -> Array call each method will return current array
   

Hash

Hash different from Array, Array use literal constructor, Hash uses key-value.

1. Create a new Hash, Ruby always use symbol to be key, like :foo, :bar
   here has two kinds of code style below.

     irb(main):001:0> song = {title: 'Kumpas', artist: 'Moira Dela Torre'}  -> recommend
     => {:title=>"Kumpas", :artist=>"Moira Dela Torre"}
     irb(main):002:0> song = {:title => 'Kumpas', :artist => 'Moira Dela Torre'}
     => {:title=>"Kumpas", :artist=>"Moira Dela Torre"}
   

   

2. Access elements, it’s almost same with array, just need to put key.

     irb(main):001:0> song = {title: 'Kumpas', artist: 'Moira Dela Torre'}
     => {:title=>"Kumpas", :artist=>"Moira Dela Torre"}
     irb(main):002:0> song[:title]
     => "Kumpas"
     irb(main):003:0> song[:artist]
     => "Moira Dela Torre"
     irb(main):004:0> song[:year]
     => nil
   

3. Hash iterate by .each, hash in block with two variable, key and value. the usage almost same with Array.

     irb(main):001:0> song = {title: 'Kumpas', artist: 'Moira Dela Torre'}
     => {:title=>"Kumpas", :artist=>"Moira Dela Torre"}
     irb(main):002:0> song.each do |key, value|
     irb(main):003:1* puts "#{key}: #{value}"
     irb(main):004:1> end
     title: Kumpas
     artist: Moira Dela Torre
     => {:title=>"Kumpas", :artist=>"Moira Dela Torre"}