Functional Sequences


This feature blew my mind. R permits to define functional sequences.

You can use %>% to not only produce values but also to produce functions (or functional sequences)! It’s really all the same, except sometimes the function is applied instantly and produces a result, and sometimes it is not, in which case the function itself is returned.1

Here is an example.


# Defining the functional sequence 
prepare <- . %>%
  group_by(year, sex) %>% 
  summarise(n = sum(n))

It is another, more readable way, to define a unary function–or to define a pipeline without applying it to the data. It is possible to get back its description.

# Functional sequence with the following components:

#  1. group_by(., year, sex)
#  2. summarise(., n = sum(n))

# Use 'functions' to extract the individual functions.

It can be included in a pipeline say to apply it to different data or to make the pipeline shorter and split it in simple, understandable operations.

babynames %>% 
  prepare %>%
  ggplot() +
  geom_bar(aes(x = year, y = n, fill = sex), 
           stat = 'identity')


  1. Blog entry for magrittr 1.5 ↩︎