def keys(self):
        if self.ndims == 1:
            return [k[0] for k in self.data.keys()]
        else:
            return list(self.data.keys())
List Tags and return JSON encoded result.
dataset/ETHPy150Open ioam/holoviews/holoviews/core/ndmapping.py/MultiDimensionalMapping.keys--crossover with--dataset/ETHPy150Open SpriteLink/NIPAP/nipap-www/nipapwww/controllers/xhr.py/XhrController.list_tags