Merge arrays in Ruby/Rails

To merge (make the union of) arrays:

[1, 2, 3].union([2, 4, 6]) #=> [1, 2, 3, 4, 6] (FROM RUBY 2.6)
[1, 2, 3] | [2, 4, 6] #=> [1, 2, 3, 4, 6]

To concat arrays:

[1, 2, 3].concat([2, 4, 6]) #=> [1, 2, 3, 2, 4, 6] (FROM RUBY 2.6)
[1, 2, 3] + [2, 4, 6] #=> [1, 2, 3, 2, 4, 6]

To add element to an array:

[1, 2, 3] << 4 #=> [1, 2, 3, 4]

But it seems that you don't have arrays, but active records. You could convert it to array with to_a, but you can also do directly:

Movie.order("RANDOM()").first(3) + [@movie]

which returns the array you want.

There's two parts to this question:

1. How to "merge two arrays"? Just use the + method:

   [1,2,3] + [2,3,4]
   => [1, 2, 3, 2, 3, 4]
   

2. How to do what you want? (Which as it turns out, isn't merging two arrays.) Let's first break down that problem:

   @movie is an instance of your Movie model, which you can verify with @movie.class.name.

   @options is an Array, which you can verify with @options.class.name.

   All you need to know now is how to append a new item to an array (i.e., append your @movie item to your @options array)

   You do that using the double shovel:

   @options << @movie
   

   this is essentially the same as something like:

   [1,2,3] << 4
   => [1,2,3,4]
   

Well, If you have an element to merge in an array you can use <<:

Eg: array = ["a", "b", "c"],  element = "d"
array << element 
=> ["a", "b", "c", "d"]

Or if you have two arrays and want duplicates then make use of += or simply + based on your requirements on mutability requirements:

Eg: array_1 = [1, 2], array_2 = [2, 3]
array_1 += array_2
=> [1, 2, 2, 3]

Or if you have two arrays and want to neglect duplicates then make use of |= or simply |:

Eg: array_1 = [1, 2], array_2 = [2, 3]
array_1 |= array_2
=> [1, 2, 3] 

@movie isn't an array in your example, it is just a single instance of a movie. This should solve your problem:

@options << @movie