class_docstr: Calculate rank order of the values in a column.
  
  Uses the "competition" ranking method: if there are four values and the
  middle two are tied, then the output will be `[1, 2, 2, 4]`.
  
  Null values will always be ranked last.
  
  :param column_name:
      The name of the column to rank.
  :param comparer:
      An optional comparison function. If not specified ranking will be
      ascending, with nulls ranked last.
  :param reverse:
      Reverse sort order before ranking.
code: def __init__(self, column_name, comparer=None, reverse=None):
      self._column_name = column_name
      self._comparer = comparer
      self._reverse = reverse
  
file_path: agate/agate/computations/rank.py
imports: from decimal import Decimal
  from functools import cmp_to_key
  from agate.computations.base import Computation
  from agate.data_types import Number
label_desc: Use image node_id 1 to create a new Rank object from inherited base classes: Computation with example: obj = Rank(column_name, comparer, reverse)