In the previous chapter, you learned the basics of transforming data. Basically you read data from some file, did some transformation to the data, and sent the data back to a different output. This is the simplest scenario. Think of a different situation. Suppose you collect results from a survey. You receive several files with the data and those files have different formats. You have to merge those files somehow and generate a unified view of the information. You also want to put aside the rows of data whose content is irrelevant. Finally, based on the rows that interest you, you want to create another file with some statistics. This kind of requirement is very common. In this chapter you will learn how to implement it with PDI.