code: def diff(f, c, n=1):
      r"""Calculate the n-th order difference for the given variable.
  
      Parameters
      ----------
      f : pandas.DataFrame
          Dataframe containing the column ``c``.
      c : str
          Name of the column in the dataframe ``f``.
      n : int
          The number of times that the values are differenced.
  
      Returns
      -------
      new_column : pandas.Series (float)
          The array containing the new feature.
  
      """
      new_column = np.diff(f[c], n)
      return new_column
  
imports: from alphapy.calendrical import biz_day_month
  from alphapy.calendrical import biz_day_week
  from alphapy.globals import NULLTEXT
  from alphapy.globals import BSEP, PSEP, USEP
  from alphapy.variables import vexec
  import itertools
  import logging
  import math
  import numpy
  import pandas
label_desc: Use image node_id 6 for calling a global function with example usage: diff(f, c, n) and returns: new_column