Ruby Array Initialization

How to initialize an array in one step using Ruby?

You can use an array literal:

array = [ '1', '2', '3' ]

You can also use a range:

array = ('1'..'3').to_a  # parentheses are required
# or
array = *('1'..'3')      # parentheses not required, but included for clarity

For arrays of whitespace-delimited strings, you can use Percent String syntax:

array = %w[ 1 2 3 ]

You can also pass a block to Array.new to determine what the value for each entry will be:

array = Array.new(3) { |i| (i+1).to_s }

Finally, although it doesn't produce the same array of three strings as the other answers above, note also that you can use enumerators in Ruby 1.8.7+ to create arrays; for example:

array = 1.step(17,3).to_a
#=> [1, 4, 7, 10, 13, 16]

Initialize method with array in Ruby

You have multiple ways of solving your problem :

• First friends could be array of names (string)

class User
    attr_accessor :name, :friends

    def initialize(name, friends)
        @name = name
        @friends = friends
    end

    def friendNbr
        return friends.count
    end

    def isFriendWith(value)
        friends.each do |friend_name|
            if (friend_name == value)
                return "Yes, #{name} is friend with #{friend_name}"
            end
        end

        return "No, #{name} is not friend with #{friend_name}"
    end
end

jane = User.new("Jane", ["Boris", "Francois", "Carlos", "Alice"])

bob = User.new("Bob", ['Jane', 'Boris', 'Missy'])

alice = User.new("Alice", ['Bob', 'Jane'])


bob.isFriendWith("Jane")
jane.isFriendWith("Alice")
alice.isFriendWith("Carlos")

• Other way is to pass object as you did but in this case you can only pass object already instanciated. In this second choice you can add a method addFriend and first create User and then add them friends.

class User
    attr_accessor :name, :friends

    def initialize(name, friends)
        @name = name
        @friends = friends
    end

    def friendNbr
        return friends.count
    end

    def isFriendWith(value)
        friends.each do |user|
            if (user.name == value)
                return "Yes, #{name} is friend with #{user.name}"
            end
        end

        return "No, #{name} is not friend with #{value}"
    end

    def addFriend(...)
      ...
    end

end

jane = User.new("Jane", [])

bob = User.new("Bob", [jane])

alice = User.new("Alice", [bob, jane])


bob.isFriendWith("Jane")
jane.isFriendWith("Alice")
alice.isFriendWith("Carlos")

Ruby Array Initialization

Arguments are always evaluated prior to a method call whereas a block is evaluated only during the method call at a timing controlled by the method (if it is ever evaluated).

In your first example, the argument "abc" is evaluated once before the method new is called. The evaluated object is passed to the method new. The exact same object is used in the all three elements of the created array. Modifying one means modifying all of them.

In your second example, the block {"abc"} is evaluated each time a new element is generated for the array. The three elements in the created array are different objects.

How to Initialize Class Arrays in Ruby

You need to use initialize as a constructor as below code and is there any reason why not to use initialize/constructor. And please fix a typo error in class definition Class Something to class Something no camel case or first letter capitalize while in class

class Something 
      def initialize
        @something = Array.new
      end
      def dosomething
        s = 5
        @something << s
      end
    end

class variable @@ are available to the whole class scope. so they are working in the code and if you want to use instance variable @ you need to initialize it as above. The instance variable is share with instance/objects of a class

for more details visit the link Ruby initialize method

Initialize an Array with optional elements depending on conditions

I'm not sure if this is a good way of doing it, but here's my suggestion:

array = [
  "1st element",
  flag? ? "2nd element" : nil,
  "3rd element"
].compact

.compact will remove all the nil values from your array. This will be problematic if you might have nil values.

Ruby array initialize on read

Something like:

a[12] = (a[12] ||= 0) + 1

How to initialise multiple array in single line in Ruby?

if I return it like [[],[]] it is working fine but in the later case, 3 arrays will get initialize which I want to avoid?

It cannot be avoided because a method can only return a single object.

So wrapping the objects in [...] is just fine:

def fetch_group_dept_values
  if condition
    [[1, 2, 3,], [4, 5]]
  else  
    [[9, 15], [10, 11]]
  end
end

The overhead of creating a (small) extra array is negligible.

However, you could avoid the outer array by yielding the values instead of returning them:

def fetch_group_dept_values
  if condition
    yield [1, 2, 3,], [4, 5]
  else  
    yield [9, 15], [10, 11]
  end
end

And call it via:

fetch_group_dept_values do |groups, departments|
  # ...
end

Ruby: how to initialize an array across several lines

You will want to put the comma, after the item like so

myarray = [
  "string 1",
  "string 2",
  "string 3"
]

Also, if you might be thinking of putting the comma before the item, for say easy commenting or something like that while your working out your code. You can leave a hanging comma in there with no real adverse side effects.

myarray_comma_ended = [
  "test",
  "test1",
  "test2", # other langs you might have to comment out this comma as well
  #"comment this one"
]

myarray_no_comma_end = [
  "test",
  "test1",
  "test2"
]

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