Ruby map! function and nested array

Question

I need to find the distance between the 2nd and 3rd elements of each nested element so

nested_array = [[0, 3, 4], [1, 20, 21], [2, 2, 2]]

def pythag_theorem(a, b)
    c = (a * a) + (b * b)
    result = Math.sqrt(c)
    result
end

def find_distance(array)
  t = 0
  while t < array.length
    array[t].map! {|x| pythag_theorem(x[1], x[2])}
  t += 1
  end
array
end

print find_distance(nested_array)

I'm getting

[[0.0, 1.4142135623730951, 0.0], [1.0, 0.0, 1.0], [1.0, 1.0, 1.0]]

when I need

[[0, 5], [1, 29], [2, 2.82842712474619]]

pythag_theorem works but why isn't map! working for me? Thanks.

Answer 1

a = [[0, 3, 4], [1, 20, 21], [2, 2, 2]]
a.map {|x,y,z| [x, Math.sqrt(y*y + z*z)]}
# => [[0, 5.0], [1, 29.0], [2, 2.82842712474619]]

Answer 2

Map does the loop for you. You don't need the while loop. You also probably shouldn't modify the the array with map!.

array = [[0, 3, 4], [1, 20, 21], [2, 2, 2]]
array.map { |(_, a, b)| Math.sqrt(a * a + b * b) }
# => [5.0, 29.0, 2.8284271247461903] 

Answer 3

This should work for you:

def find_distance(array)
  array.map do |tuple|
    [tuple[0],pythag_theorem(tuple[1],tuple[2])]
  end
end

BTW it is not a good idea to modify a function argument in place.