Generate non-repeating random numbers in Ruby

a = (100..999).to_a.shuffle 

then every time you need a new id

new_id = a.pop

This guarantees that numbers are never reused. Of course, you'll have problems when you run out of elements on the array.

Notice that the last statement in your method is the while loop, which will not execute if products is empty. Hence function returns nil.

Try like this:

products = {}

def random_key(products)

  rand_key = rand(900) + 100

  while products.has_key?(rand_key)

    rand_key = rand(900) + 100

  end

  rand_key

end

puts random_key(products)

Note however, that this has a potential of getting into an infinite loop once all numbers from 100 to 999 are in products

Your function returns the while expression which is always nil. You should return the number instead:

def random_key(products)
  rand_key = rand(900) + 100
  while products.has_key?(rand_key)
    rand_key = rand(900) + 100
  end
  rand_key
end

Note that you can remove duplication by placing "while" after key generation:

def random_key(products)
  begin
    rand_key = rand(900) + 100
  end while products.has_key?(rand_key)
  rand_key
end

And you can omit begin end for a single expression

def random_key(products)
  rand_key = rand(900) + 100 while products.has_key?(rand_key)
  rand_key
end

I believe the Marc Talbot answer is great! But put the answer in your context, let's explain a bit,

First, creates the ids.

ids = (100..999).to_a.shuffle 

Now, you can avoid the while, the method, the has_key?, and so on, and just call ids.pop

products[ids.pop] = {}

The final code version is:

ids = (100..999).to_a.shuffle 
products[ids.pop] = {}

The result will be:

irb(main):023:0> products[ids.pop] = {}
=> {}
irb(main):024:0> products[ids.pop] = {}
=> {}
irb(main):025:0> products[ids.pop] = {}
=> {}
irb(main):026:0> products[ids.pop] = {}
=> {}
irb(main):027:0> products
=> {554=>{}, 968=>{}, 665=>{}, 181=>{}}