Generate combinations of values from multiple arrays

Question

I have four arrays of equal length:

a = [1, 2, 3, 4, 5]
b = ['A', 'B', 'C', 'D', 'E']
c = ['J', 'K', 'L', 'M', 'N']
d = ['v', 'w', 'x', 'y', 'z']

and I want to get an array of all possible combination by taking one element from each of the arrays:

[
  [1, 'A', 'J', 'v'], 
  [2, 'A', 'J', 'v'], 
  [3, 'A', 'J', 'v'],
  ...
]

I'm doing this:

master_array = []

for i in first_names do
    sub_array = []
    for j in last_names do
        for k in city do
            for l in state do
                sub_array.push(i, j, k, l)
            end
        end
    end
    master_array.push(sub_array)
end

master_array

Ideally I would like to return an array of hashes, whose keys are the names of the arrays, like so:

[
  {a: 1, b: 'A', c: 'J', d: 'v'}, 
  {a: 2, b: 'A', c: 'J', d: 'v'}, 
  {a: 3, b: 'A', c: 'J', d: 'v'},
  ...
]

Answer 1

Use Array#product, as @sagarpandya suggests.

def get_em_all(a, *arr)
  a.product(*arr)
end

get_em_all(a, b, c, d)
  # => [[1, "A", "J", "v"], [1, "A", "J", "w"], [1, "A", "J", "x"], [1, "A", "J", "y"],
  #     [1, "A", "J", "z"], [1, "A", "K", "v"], [1, "A", "K", "w"], [1, "A", "K", "x"],
  #     ...
  #     [5, "E", "N", "w"], [5, "E", "N", "x"], [5, "E", "N", "y"], [5, "E", "N", "z"]]

get_em_all(a, b, c, d).size
  #=> 625 (= 5**4)

Note that if the arguments of get_em_all are changed to something else--8 3-element arrays, for example----no change is required to the method.

Objects, such as arrays, do not know the variable or variables that hold them. Consider, for example,

a = [1,2,3]
b = a
  #=> [1, 2, 3]
a.object_id
  #=> 4303360
b.object_id
  #=> 4303360

Both the variable a and the variable b old the same object, the array [1,2,3].

Therefore, to obtain the array of hashes you want you would have to construct it at compile time with keys that are literals, hardwired to the four arrays a, b, c, and k. Moreover, there's no reason to use names of variables as the hash's keys. That would be bad bad programming practice on several levels.

Answer 2

If you want all the possible combinations, there's no alternative other than iterating through each of the elements for all arrays.

Creating hashes is not difficult either.

Try this.

a = [1, 2, 3, 4, 5]
b = ['A', 'B', 'C', 'D', 'E']
c = ['J', 'K', 'L', 'M', 'N']
d = ['v', 'w', 'x', 'y', 'z']

result = []

a.each do |a_elem|
  b.each do |b_elem|
    c.each do |c_elem|
      d.each do |d_elem|
        result << {a: a_elem, b: b_elem, c: c_elem, d: d_elem}
      end
    end
  end
end

puts "#{result}"

I believe this is what you are looking for.