ABSTRACT
This chapter introduces in simple terms how R language processes data, including the frequently used data processing operations like looping, grouping, merging, pipeline, word segmentation, etc. The family of apply functions is a group of core functions for data processing in R language. Lapply function is one of the most basic loop operation functions. It is used to loop the datasets of list and data. The sapply function is a simplified lapply. Mapply function is the deforming function of sapply. It is similar to the sapply function with multiple variables but different in the parameter definition. Tapply function is used to do loop computing for groups. Dataset X can be grouped by the INDEX parameter, functioned the same as the frequently used group by operation of SQL. Rapply function is a recursive version of lapply function. It deals with the data of list type only.
