Better support for Pandas.Series

[dorisjlee]

We should create a LuxSeries object to take on the sliced version of the LuxDataframe, following guidelines for subclassing DataFrames. We need to pass the _metadata from LuxDataFrame to LuxSeries so that it is preserved across operations (and therefore doesn't need to be recomputed), related to #65. Currently, this code is commented since LuxSeries is causing issues compared to the original Pd.Series.

class LuxDataFrame(pd.DataFrame):
        ....
	@property
	def _constructor(self):
		return LuxDataFrame

	@property
	def _constructor_sliced(self):
		def f(*args, **kwargs):
			# adapted from https://github.com/pandas-dev/pandas/issues/13208#issuecomment-326556232
			return LuxSeries(*args, **kwargs).__finalize__(self, method='inherit')
		return f

class LuxSeries(pd.Series):
	# _metadata =  ['name','_intent','data_type_lookup','data_type',
	# 			 'data_model_lookup','data_model','unique_values','cardinality',
	# 			'min_max','plot_config', '_current_vis','_widget', '_recommendation']
	def __init__(self,*args, **kw):
		super(LuxSeries, self).__init__(*args, **kw)
	@property
	def _constructor(self):
		return LuxSeries

	@property
	def _constructor_expanddim(self):
		from lux.core.frame import LuxDataFrame
		# def f(*args, **kwargs):
		# 	# adapted from https://github.com/pandas-dev/pandas/issues/13208#issuecomment-326556232
		# 	return LuxDataFrame(*args, **kwargs).__finalize__(self, method='inherit')
		# return f
		return LuxDataFrame

In particular the original name property of the Lux Series is lost when we implement LuxSeries, see test_pandas.py:test_df_to_series for more details.
Example:

df = pd.read_csv("lux/data/car.csv")
df._repr_html_()
series = df["Weight"]
series.name # returns None (BUG!)
series.cardinality # preserved

We should also add a repr to print out the basic histogram for Series objects.

[dorisjlee]

Support for Pandas Series is much more robust now with these changes. Thanks @westernguy2 !