'Uses axis.unit_data map to encode
data as floats'

@staticmethod
def convert(value, unit, axis):

    vmap = dict(zip(axis.unit_data.seq, axis.unit_data.locs))
    if isinstance(value, six.string_types):
        return vmap[value]
    vals = shim_array(value)
    for (lab, loc) in vmap.items():
        vals[(vals == lab)] = loc
    return vals.astype(u'float')
