docstr: Create mapping between unique categorical values and integer ids.
  
  Parameters
  ----------
  data : iterable
      sequence of string values
docstr_tok: ["Create","mapping","between","unique","categorical","values","and","integer","ids",".","Parameters","--","--","--","--","--","data",":","iterable","sequence","of","string","values"]
code: def __init__(self, data=None):
      """
      Create mapping between unique categorical values and integer ids.
  
      Parameters
      ----------
      data : iterable
          sequence of string values
      """
      self._mapping = OrderedDict()
      self._counter = itertools.count()
      if data is not None:
          self.update(data)
  
imports: from collections import OrderedDict
  import dateutil.parser
  import itertools
  import logging
  import numpy
  from matplotlib import _api, ticker, units
label_desc: Use image node_id 1 to create a new UnitData object  with example: obj = UnitData(data)