Add element to an array if it's not there already

Question

I have a Ruby class

class MyClass
  attr_writer :item1, :item2
end

my_array = get_array_of_my_class() #my_array is an array of MyClass
unique_array_of_item1 = [         


        

Answer 1

@Coorasse has a good answer, though it should be:

my_array | [item]

And to update my_array in place:

my_array |= [item]

Answer 2

Important to keep in mind that the Set class and the | method (also called "Set Union") will yield an array of unique elements, which is great if you want no duplicates but which will be an unpleasant surprise if you have non-unique elements in your original array by design.

If you have at least one duplicate element in your original array that you don't want to lose, iterating through the array with an early return is worst-case O(n), which isn't too bad in the grand scheme of things.

class Array
  def add_if_unique element
    return self if include? element
    push element
  end
end

Answer 3

You can use Set instead of Array.

Answer 4

I'm not sure if it's perfect solution, but worked for me:

    host_group = Array.new if not host_group.kind_of?(Array)
    host_group.push(host)

Answer 5

You don't need to iterate through my_array by hand.

my_array.push(item1) unless my_array.include?(item1)

Edit:

As Tombart points out in his comment, using Array#include? is not very efficient. I'd say the performance impact is negligible for small Arrays, but you might want to go with Set for bigger ones.

Answer 6

You can convert item1 to array and join them:

my_array | [item1]