def get_tag2idx(df):
	"""
	Returns tags maps from a given dataframe df
	Outputs:
		tag2idx: map from tag to idx
		idx2tag: map from idx to tag
	"""
	tag_values = list(df["tag"].unique()) + ['PAD']
	tag2idx = {tag:idx for idx, tag in enumerate(tag_values)}
	idx2tag = {idx:tag for tag, idx in tag2idx.items()}
	return tag2idx, idx2tag