docstr: Create mapping between unique categorical values
  and integer identifiers
  ----------
  data: iterable
        sequence of string values
docstr_tok: ["Create","mapping","between","unique","categorical","values","and","integer","identifiers","--","--","--","--","--","data",":","iterable","sequence","of","string","values"]
code: def __init__(self, data=None):
      """Create mapping between unique categorical values
      and integer identifiers
      ----------
      data: iterable
            sequence of string values
      """
      self._mapping = OrderedDict()
      self._counter = itertools.count(start=0)
      if data is not None:
          self.update(data)
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from collections import OrderedDict
  import itertools
  import six
  import numpy
  import matplotlib.units
  import matplotlib.ticker
  from distutils.version import LooseVersion
label_desc: Use image node_id 1 to create a new UnitData object from inherited base classes: object with example: obj = UnitData(data)