iterating over an array with index position in Ruby

Question

I'm doing prepwork for a course in which one of the challenges (which I failed, miserably) went something along the lines of:

Define a method that takes an array and multiplies each value in the array by its position in the array.

So basically, array = [1, 2, 3, 4, 5] should return 1*0, 2*1, 3*2, 4*3, 5*4.

I'm having a lot of trouble figuring out how to do it. I don't think they intended for us to use .inject or .reduce or anything but the bare basics.

This is what I've managed to do so far, but it doesn't run:

array = [1,2,3,4,5]

def calculator (arr)
new_arr = []
new_arr = arr.each_with_index {|value, index| value * index}
end

calculator(array)

I've tried some variations with .collect, and various parameters. Sometimes I get parameter errors or the array returned to me with nothing modified.

I would really appreciate an explanation or any advice!

Answer 1

[1, 2, 3, 4, 5].map.with_index(&:*)

Answer 2

If you wanted something super basic:

def calculator (array)
  count = 0
  new_array = []
  array.each do |number|
    new_array<<number*count
    count +=1
    end
  return new_array
end

It's not the most "clean" way but does help you walk through the problem :)

Answer 3

To me best and easiest way is:

result = [1, 2, 3, 4, 5].each_with_index.map {|value, index| value * index}

Which results in:

[0, 2, 6, 12, 20] 

Or in another way without using map you can do:

[1, 2, 3, 4, 5].each_with_index do |value, index| 
    puts value * index 
end