Simple Parser Ruby

def calculate(string)
  splitted = split_string_by_operators(string)
  parsed = parse_to_nums(splitted)
  splitted = split_by_minus_or_plus(parsed)
  almost_end = splitted.map! {|elem| eval_each_three(elem)}.flatten!
  eval_each_three(almost_end)
end

def split_string_by_operators(string)
  string.split(%r{(\+|\-|\/|\*)}).map do |x|
    unless x =~ /(\+|\-|\/|\*)/
      x.to_f
    else
      x
    end
  end
end

def split_by_minus_or_plus(array)
  result = []
  second_prior_operators = array.count("+") + array.count('-')
  (second_prior_operators+1).times do
    result << []
  end
  ind = 0
  array.each do |token|
    if token != "+" || token != '-'
      result[ind].push(token)
      p result
    else
      result.insert(ind, token)
      #puts result
      ind += 1
    end
  end
  result

end


def eval_each_three(ary)
  result = 0
  while ary.size != 1
    result = calc(ary[0], ary[1], ary[2])
    3.times do
      ary.shift
    end
    ary.unshift(result)
  end
  ary
end

#[982.0, "*", 5.0, "+", 3.0, "/", 5.0, "-", 1.0]

def calc(num1, operator, num2)
  case operator
    when  "*"
      num1 * num2
    when  "-"
      num1 - num2
    when  "/"
      num1.to_f / num2
    when  "+"
      num1 + num2
  end
end

def parse_to_nums(ary)
  ary.map! do |token|
    if token =~ /\d/
      token.to_i
    else
      token
    end
  end
end