end FUNCTION parse() 
FUNCTION: transform()
Returns a data transformation function.

@private
@returns {function} data transformation function
function transform() {
		var kde = new KDE();
		/**
		* FUNCTION: transform( data )
		*	Defines the data transformation.
		*
		* @private
		* @param {number} data - numeric stream data
		* @returns {number} transformed data
		*/
		return function transform( data ) {
			kde.estimator( data, 'silverman' );
			return kde.eval( data );
		};
	}