R Operator - Pipe

A pipe operator passes the output of the last command to the next command, like | in Shell. A pipe operator simplifies two steps

1. Assign the result to a variable
   • When using a pipe operator, the output will not be printed to the stdout
2. Pass the variable to a command/function
   • When piping into a function, its first argument can be omitted

%>%, a famous pipe operator in R introduced by magrittr¹ package, is widely used by many R Packages, like dplyr.

An Example

mtcars %>% 
    filter(mpg > 25) %>%
    arrange(desc(mpg)) %>%
    ggplot(data=.,aes(x=row.names(.), y=mpg)) +
        geom_bar(stat="identity")

Behind the scenes, x %>% f(y) turns into f(x, y), and x %>% f(y) %>% g(z)turns into g(f(x, y), z) and so on.

The pipe operator enable us to focus on the transformations, not what’s being transformed. It also makes the code easier to read: replace %>% with “then” when reading code.

In R 4.1, a built-in pipe operator is introduced: |>. This operator doesn’t rely on third-party packages and may be faster. But it lacks two important features that %>% has

• represent the value being piped in by ., as in the above example
• when you pipe into a function with no other arguments, you can omit the parentheses ()

Footnotes

1. Rene Magritte has a famous painting that says “This is not a pipe.” ↩