Ruby: got TypeError when calling function. What's happening?

Question

I am a ruby newbie and have a problem with getting the code below to work

def factorial(n)
  if n == 0
    1
  else
    n * factorial(n-1)
  end
end

puts factorial(numbers)

I keep getting the error message can't convert Fixnum into Array (TypeError) in `factorial'. Anyone able to help me with answer to what I am doing wrong in this case? Thanks in advance

Answer 1

I don't know any Ruby, but I suspect that numbers is an array of numbers, not just one, and when you pass it to factorial it tries to perform the computation and blows up. (It doesn't make sense to compare an array to zero, multiply it, or subtract it.)

You'll need to either change factorial to accept multiple numbers and find the factorial of each, or (easier) change the calling code to compute one factorial at a time over the set of numbers.

Answer 2

As mquander says, numbers is apparently an array.

So what you need is something like:

puts(numbers.map { |n| factorial(n) })

And, incidentally, your error has nothing to do with recursion.

Confirming mquander's theory:

> numbers = [1,2,3]
> puts factorial(numbers)
TypeError: can't convert Fixnum into Array

And just out of curiosity, here's how you implement factorial in ruby without recursion, so that you don't get a stack overflow for large numbers.

def factorial(n)
  (1..n).inject(1) { |ac, x| ac * x }
end

Answer 3

you are probably looking for something like:

numbers.map { |n| factorial(n) }

Answer 4

As an addition to kch's code, you can modify the function to handle both array and scalar input.

def factorial(n)
  if n.is_a?(Array)
    return n.map {|n| factorial(n)}
  end
  raise unless n.is_a?(Integer) and (n >= 0)
  (n == 0) ? 1 : n * factorial(n-1)
end

This functions handles scalars, arrays, nested arrays, invalid things, etc.

Edit: Incorporated kch's simplified type-checking code