text: from typing import Union
  
  import numpy as np
  import talib
  
  from jesse.helpers import get_candle_source
  
  
  def efi(candles: np.ndarray, period: int = 13, source_type: str = "close", sequential: bool = False) -> Union[
      float, np.ndarray]:
      """
      EFI - Elders Force Index
  
      :param candles: np.ndarray
      :param period: int - default: 13
      :param source_type: str - default: "close"
      :param sequential: bool - default=False
  
      :return: float | np.ndarray
      """
      if not sequential and len(candles) > 240:
          candles = candles[-240:]
  
      source = get_candle_source(candles, source_type=source_type)
  
      dif = np.zeros(len(source) - 1)
      for i in range(1, len(source)):
          dif[i - 1] = (source[i] - source[i - 1]) * candles[:, 5][i]
  
      res = talib.EMA(dif, timeperiod=period)
      res_with_nan = np.concatenate((np.full((candles.shape[0] - res.shape[0]), np.nan), res))
  
      return res_with_nan if sequential else res_with_nan[-1]
  