class_docstr: Select a fixed number of test rows per user/item, based on ordering by a
  column.
  
  Args:
      n(int): The number of test items to select.
class_docstr_tok: ["Select","a","fixed","number","of","test","rows","per","user\/item",",","based","on","ordering","by","a","column",".","Args",":","n","(","int",")",":","The","number","of","test","items","to","select","."]
code: def __init__(self, n, col="timestamp"):
      self.n = n
      self.column = col
  
imports: from collections import namedtuple
  import logging
  from abc import ABC, abstractmethod
  import numpy
  import pandas
  from seedbank import numpy_rng
label_desc: Use image node_id 1 to create a new LastN object from inherited base classes: PartitionMethod with example: obj = LastN(n, col)