Hao Ren is data engineer working in Paris for a classified advertising website named leboncoin (https://www.leboncoin.fr/), which is the fifth most visited site in France. Three years' work experience of functional programming in Scala, Machine Learning, and distributed systems defines his career. Hao's main speciality is based on machine learning with Apache Spark, such as building a crawler detection system, recommander system, and so on. He has also reviewed a more detailed and advanced book by Packt Publishing, Machine Learning with Spark, which is worth a read as well.