R Language Pipe operators (%>% and others) Functional sequences
Example
Given a sequence of steps we use repeatedly, it's often handy to store it in a function. Pipes allow for saving such functions in a readable format by starting a sequence with a dot as in:
. %>% RHS
As an example, suppose we have factor dates and want to extract the year:
library(magrittr) # needed to include the pipe operators
library(lubridate)
read_year <- . %>% as.character %>% as.Date %>% year
# Creating a dataset
df <- data.frame(now = "2015-11-11", before = "2012-01-01")
# now before
# 1 2015-11-11 2012-01-01
# Example 1: applying `read_year` to a single character-vector
df$now %>% read_year
# [1] 2015
# Example 2: applying `read_year` to all columns of `df`
df %>% lapply(read_year) %>% as.data.frame # implicit `lapply(df, read_year)
# now before
# 1 2015 2012
# Example 3: same as above using `mutate_all`
library(dplyr)
df %>% mutate_all(funs(read_year))
# if an older version of dplyr use `mutate_each`
# now before
# 1 2015 2012
We can review the composition of the function by typing its name or using functions:
read_year
# Functional sequence with the following components:
#
# 1. as.character(.)
# 2. as.Date(.)
# 3. year(.)
#
# Use 'functions' to extract the individual functions.
We can also access each function by its position in the sequence:
read_year[[2]]
# function (.)
# as.Date(.)
Generally, this approach may be useful when clarity is more important than speed.
