Pipe

Pipe() creates a Pipe object where built-in symbols are designed for building pipeline.

• $ chains functions by first-argument piping and always returns a Pipe object.
• .(...) evaluates an expression with . or by lambda expression, or for side effect, or simply extract a named element. The usage is exactly the same with x %>>% (...).
• Subsetting, extracting, and assigning with Pipe on its inner value and Pipe object is preserved.
• $value or [] extracts the final value of the Pipe object.

Usage

Pipe as first-argument to a function:

Pipe(rnorm(100,mean=10))$
  log()$
  diff()$
  plot(col="red")

Pipe by lambda expression

Pipe(mtcars)$
  .(lm(mpg ~ ., data = .))$
  summary() []

Pipe(mtcars)$
  .(df ~ lm(mpg ~ ., data = df))$
  summary() []

Pipe for extracting element

Pipe(mtcars)$
  .(mpg)$
  summary() []

Pipe for side effect

Pipe(iris)$
  .(~ cat(length(.), "columns","\n"))$
  .(~ plot(.))$
  summary()

Subsetting Pipe object

Pipe(mtcars)["mpg"]

Extracting from Pipe object

Pipe(mtcars)[["mpg"]]

Assigning to Pipe object's element

plist <- Pipe(list(a=1,b=2))
plist$a <- 0
plist$b <- NULL

plist <- Pipe(list(a=1,b=2))
plist["a"] <- 2
plist[["b"]] <- 3

If the Pipe object is used in more than one pipelines, a recommended usage is to name the object specially so that it is easy to distinguish the Pipe object from the value it stores. For example, it can start with p, as shown above.

Stored Pipe object

Pipe can also be stored as function.

f1 <- Pipe(rnorm(100))$plot
f1(col="red")
f1(col="green")

When the arguments are supplied, plot() will be evaluated. Although Pipe is lazy but its value is determined at first evaluation.