The magrittr package offers a set of operators which promote semantics
  that will improve your code by

  * structuring sequences of data operations left-to-right (as
    opposed to from the inside and out),
  * avoiding nested function calls,
  * minimizing the need for local variables and function
    definitions, and
  * making it easy to add steps anywhere in the sequence of operations.

  WWW: http://cran.r-project.org/web/magrittr/