In this post,we will state the use of pipes in R, includes %>%, %$%, %T>%, %<>% and |>.

First let’s construct some data for a demonstration of pipes usage in R (PS: The ideas and example data for this post came from this dplyr github issue):

packageVersion('magrittr')

## [1] '2.0.3'

library(magrittr)

exampledt = tibble::tibble(
  BP = c("-", "-", "A", "B"),
  CL = c("-", "C", "-", "D"),
  MF = c("-", "-", "-", "E")
) %>% 
  {. == '-'} %>% 
  tibble::as_tibble()
exampledt

## # A tibble: 4 × 3
##   BP    CL    MF   
##   <lgl> <lgl> <lgl>
## 1 TRUE  TRUE  TRUE 
## 2 TRUE  FALSE TRUE 
## 3 FALSE TRUE  TRUE 
## 4 FALSE FALSE FALSE

Pipes in magrittr

%>% most commonly used magrittr pipe

Basic piping

  • x %>% f is equivalent to f(x)
  • x %>% f(y) is equivalent to f(x, y)
  • x %>% f %>% g %>% h is equivalent to h(g(f(x)))

Argument placeholder

(Suppose f has only two parameters)

  • x %>% f(y, .) is equivalent to f(y, x)
  • x %>% f(y, z = .) is equivalent to f(y, z = x)

Re-using the placeholder for attributes

(Suppose f has three parameters,and y and z are not its first parameter)

  • x %>% f(y = nrow(.), z = ncol(.)) is equivalent to f(x, y = nrow(x), z = ncol(x))

  • x %>% {f(y = nrow(.), z = ncol(.))} is equivalent to f(y = nrow(x), z = ncol(x))

Building (unary) functions

f = . %>% cos %>% sin is equivalent to f = function(.) sin(cos(.))

Usuage

exampledt %>% 
  dplyr::mutate(col3sum = rowSums(.))

## # A tibble: 4 × 4
##   BP    CL    MF    col3sum
##   <lgl> <lgl> <lgl>   <dbl>
## 1 TRUE  TRUE  TRUE        3
## 2 TRUE  FALSE TRUE        2
## 3 FALSE TRUE  TRUE        2
## 4 FALSE FALSE FALSE       0

exampledt %>% 
  dplyr::mutate(.,col3sum = rowSums(.))

## # A tibble: 4 × 4
##   BP    CL    MF    col3sum
##   <lgl> <lgl> <lgl>   <dbl>
## 1 TRUE  TRUE  TRUE        3
## 2 TRUE  FALSE TRUE        2
## 3 FALSE TRUE  TRUE        2
## 4 FALSE FALSE FALSE       0

exampledt %>% 
  dplyr::mutate({col3sum = rowSums(.)})

## # A tibble: 4 × 4
##   BP    CL    MF    `{ ... }`
##   <lgl> <lgl> <lgl>     <dbl>
## 1 TRUE  TRUE  TRUE          3
## 2 TRUE  FALSE TRUE          2
## 3 FALSE TRUE  TRUE          2
## 4 FALSE FALSE FALSE         0

exampledt %>% 
  dplyr::mutate(col3sum = {rowSums(.)})

## # A tibble: 4 × 4
##   BP    CL    MF    col3sum
##   <lgl> <lgl> <lgl>   <dbl>
## 1 TRUE  TRUE  TRUE        3
## 2 TRUE  FALSE TRUE        2
## 3 FALSE TRUE  TRUE        2
## 4 FALSE FALSE FALSE       0

exampledt %>% 
  rowSums() %>% 
  {. != 3} %>% 
  sum()

## [1] 3

exampledt %>% 
  rowSums() %>% 
  sum(. != 3)

## [1] 10

exampledt %>% 
  rowSums() %>% 
  sum({. != 3})

## [1] 10

exampledt %>% 
  rowSums() %>% 
  {sum(. != 3)}

## [1] 3

%$% pipe with exposition of variables

The “exposition” pipe, %$% exposes the names within the left-hand side object to the right-hand side expression. Essentially, it is a short-hand for using the with functions (and the same left-hand side objects are accepted). This operator is handy when functions do not themselves have a data argument, as for example lm and aggregate do. Here are a few examples as illustration:

iris %>%
  dplyr::filter(Sepal.Length > mean(Sepal.Length)) %$%
  cor(Sepal.Length, Sepal.Width)

## [1] 0.3361992

%T>% pipe returns the left-hand side value

The “tee” pipe, %T>% works like %>%, except it returns the left-hand side value, and not the result of the right-hand side operation. This is useful when a step in a pipeline is used for its side-effect (printing, plotting, logging, etc.).

rnorm(200) %>%
matrix(ncol = 2) %T>%
plot %>% # plot usually does not return anything. 
colSums()

## [1] -0.449311 13.174459

%<>% as the first pipe in a chain

The “assignment” pipe %<>% can be used as the first pipe in a chain. The effect will be that the result of the pipeline is assigned to the left-hand side object, rather than returning the result as usual.The %<>% can be used whenever expr = … makes sense, e.g.

  • foo = foo %>% bar %>% baz boils down to foo %<>% bar %>% baz
  • x[1:10] %<>% foo %>% bar
  • x$baz %<>% foo %>% bar

|> pipe in baseR

Basic piping

  • x |> f() is equivalent to f(x)
  • x |> f(y) is equivalent to f(x, y)
  • x |> f() |> g() |> h() is equivalent to h(g(f(x)))

Argument placeholder

  • must use the _ placeholder with a named argument
  • x %>% f(y, z = _) is equivalent to f(y, z = x)
  • x %>% f(y, _) is not available

Usage

exampledt |> 
  _$MF

## [1]  TRUE  TRUE  TRUE FALSE

exampledt |> 
  rowSums()

## [1] 3 2 2 0

exampledt |> 
  dplyr::mutate(col3sum = rowSums(x = _))

## Error: invalid use of pipe placeholder (<text>:2:0)

Reference:

  1. https://magrittr.tidyverse.org/index.html