Merlin DAG

merlin.dag.Operator()	Base class for all operator classes.
merlin.dag.Graph(output_node)	Represents an DAG composed of Nodes, each of which contains an operator that transforms dataframes or dataframe-like data
merlin.dag.Node([selector])	A Node is a group of columns that you want to apply the same transformations to.
merlin.dag.ColumnSelector([names, ...])	A ColumnSelector describes a group of columns to be transformed by Operators in a Graph.