code: def lowest(f, c, p=20):
      r"""Calculate the lowest value on a rolling basis.
  
      Parameters
      ----------
      f : pandas.DataFrame
          Dataframe containing the column ``c``.
      c : str
          Name of the column in the dataframe ``f``.
      p : int
          The period over which to calculate the rolling minimum.
  
      Returns
      -------
      new_column : pandas.Series (float)
          The array containing the new feature.
  
      """
      return f[c].rolling(p).min()
  
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 28 for calling a global function with example usage: lowest(f, c, p) and returns: f