operator: Multiple assignment operators

In zeallot: Multiple, Unpacking, and Destructuring Assignment

Multiple assignment operators

Description

Assign values to name(s).

Usage

x %<-% value

value %->% x

Arguments

x	A name structure, see section below.
value	A list of values, vector of values, or R object to assign.

Value

%<-% and %->% invisibly return value.

These operators are used primarily for their assignment side-effect. %<-% and %->% assign into the environment in which they are evaluated.

Name Structure

The basics

At its simplest, the name structure is a single variable name, in which case %<-% and %->% perform regular assignment, x %<-% list(1, 2, 3) or list(1, 2, 3) %->% x.

To specify multiple variable names use c(), for example c(x, y, z) %<-% c(1, 2, 3).

When value is neither an atomic vector nor a list, %<-% and %->% will try to destructure value into a list before assigning variables, see destructure().

In-place assignment

One may also assign into a list or environment, c(x, x[[1]]) %<-% list(list(), 1).

Nested names

One can also nest calls to c(), c(x, c(y, z)). This nested structure is used to unpack nested values, c(x, c(y, z)) %<-% list(1, list(2, 3)).

Collector variables

To gather extra values from the beginning, middle, or end of value use a collector variable. Collector variables are indicated with the .. prefix, c(..x, y) %<-% list(1, 2, 3, 4).

Skipping values

Use . in place of a variable name to skip a value without raising an error or assigning the value, c(x, ., z) %<-% list(1, 2, 3).

Use .. to skip multiple values without raising an error or assigning the values, c(w, .., z) %<-% list(1, NA, NA, 4).

Default values

Use = with a value to specify a default value for a variable, c(x, y = NULL) %<-% list(1).

Unfortunately, using a default value with in-place assignment raises an error because of R's syntax, c(x, x[[1]] = 1) %<-% list(list()).

Named assignment

Use = without a value to assign values by name, c(two=) %<-% list(one = 1, two = 2, three = 3).

See Also

For more on unpacking custom objects please refer to destructure().

Examples

# Basic usage
c(x, y) %<-% list(0, 1)

# Unpack and assign nested values
c(c(x, y), z) %<-% list(list(2, 3), list(3, 4))

# Assign columns of data frame
c(eruptions, waiting) %<-% faithful

# Assign specific columns by name
c(mpg=, hp=, gear=) %<-% mtcars

# Alternatively, assign a column by position
c(first_col, .., last_col) %<-% mtcars

# Skip initial values, assign final value
todo_list <- list("1. Make food", "2. Pack lunch", "3. Save world")

c(.., final_todo) %<-% todo_list

# Assign first name, skip middle initial, assign last name
c(first_name, ., last_name) %<-% c("Ursula", "K", "Le Guin")

# Unpack nested values w/ nested names
fibs <- list(1, list(2, list(3, list(5))))

c(f2, c(f3, c(f4, c(f5)))) %<-% fibs

# Unpack first numeric, leave rest
c(f2, ..rest) %<-% unlist(fibs)

# Swap values without using temporary variables
c(a, b) %<-% c("eh", "bee")

c(a, b) %<-% c(b, a)

# Handle missing values with default values
parse_time <- function(x) {
  strsplit(x, " ")[[1]]
}

c(hour, period = NA) %<-% parse_time("10:00 AM")

c(hour, period = NA) %<-% parse_time("15:00")

# Right operator
list(1, 2, "a", "b", "c") %->% c(x, y, ..z)

zeallot documentation built on June 8, 2025, 1:36 p.m.