code: def test_idxmapping_apply_key_type(self):
      data = dict([(0.5, "a"), (1.5, "b")])
      ndmap = MultiDimensionalMapping(data, kdims=[self.dim1])
  
      self.assertEqual(list(ndmap.keys()), [0, 1])
  
imports: import numpy
  from holoviews import Dataset, HoloMap
  from holoviews.core import Dimension
  from holoviews.core.ndmapping import MultiDimensionalMapping, NdMapping, UniformNdMapping
  from holoviews.core.overlay import Overlay
  from holoviews.element import Curve
  from holoviews.element.comparison import ComparisonTestCase
label_desc: Use image node_id 28 for calling the NdIndexableMappingTest obj's underlying member method code with example usage: obj.test_idxmapping_apply_key_type() without return types