class_docstr: This class simply exists to hold the methods necessary for fancy indexing.
class_docstr_tok: ["This","class","simply","exists","to","hold","the","methods","necessary","for","fancy","indexing","."]
code: def _boolean_index_to_array(self, i):
      if i.ndim > 1:
          raise IndexError("invalid index shape")
      return i.nonzero()[0]
  
imports: from __future__ import division, print_function, absolute_import
  import operator
  import warnings
  import numpy
  from scipy._lib._version import NumpyVersion
label_desc: Use image node_id 5 for calling the IndexMixin obj's underlying member method code with example usage: obj._boolean_index_to_array(i) and returns: i