Multiple assignment operators
Assign values to name(s).
x %<-% value value %->% x
x |
A name structure, see section below. |
value |
A list of values, vector of values, or R object to assign. |
%<-% and %->% invisibly return value.
These operators are used primarily for their assignment side-effect.
%<-% and %->% assign into the environment in which they
are evaluated.
the basics
At its simplest, the name structure may be 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 a call to 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().
object parts
Like assigning a variable, one may also assign part of an object, c(x,
x[[1]]) %<-% list(list(), 1).
nested names
One can also nest calls to c() when needed, 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 a ...
prefix, c(...start, z) %<-% 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 = to specify a default value for a variable, c(x, y = NULL)
%<-% tail(1, 2).
When assigning part of an object a default value may not be specified because
of the syntax enforced by R. The following would raise an "unexpected '=' ..." error, c(x, x[[1]] = 1) %<-% list(list()).
For more on unpacking custom objects please refer to
destructure().
# basic usage
c(a, b) %<-% list(0, 1)
a # 0
b # 1
# unpack and assign nested values
c(c(e, f), c(g, h)) %<-% list(list(2, 3), list(3, 4))
e # 2
f # 3
g # 4
h # 5
# can assign more than 2 values at once
c(j, k, l) %<-% list(6, 7, 8)
# assign columns of data frame
c(erupts, wait) %<-% faithful
erupts # 3.600 1.800 3.333 ..
wait # 79 54 74 ..
# assign only specific columns, skip
# other columns
c(mpg, cyl, disp, ...) %<-% mtcars
mpg # 21.0 21.0 22.8 ..
cyl # 6 6 4 ..
disp # 160.0 160.0 108.0 ..
# skip initial values, assign final value
TODOs <- list("make food", "pack lunch", "save world")
c(..., task) %<-% TODOs
task # "save world"
# assign first name, skip middle initial,
# assign last name
c(first, ., last) %<-% c("Ursula", "K", "Le Guin")
first # "Ursula"
last # "Le Guin"
# simple model and summary
mod <- lm(hp ~ gear, data = mtcars)
# extract call and fstatistic from
# the summary
c(modcall, ..., modstat, .) %<-% summary(mod)
modcall
modstat
# unpack nested values w/ nested names
fibs <- list(1, list(2, list(3, list(5))))
c(f2, c(f3, c(f4, c(f5)))) %<-% fibs
f2 # 1
f3 # 2
f4 # 3
f5 # 5
# unpack first numeric, leave rest
c(f2, fibcdr) %<-% fibs
f2 # 1
fibcdr # list(2, list(3, list(5)))
# swap values without using temporary variables
c(a, b) %<-% c("eh", "bee")
a # "eh"
b # "bee"
c(a, b) %<-% c(b, a)
a # "bee"
b # "eh"
# unpack `strsplit` return value
names <- c("Nathan,Maria,Matt,Polly", "Smith,Peterson,Williams,Jones")
c(firsts, lasts) %<-% strsplit(names, ",")
firsts # c("Nathan", "Maria", ..
lasts # c("Smith", "Peterson", ..
# handle missing values with default values
parse_time <- function(x) {
strsplit(x, " ")[[1]]
}
c(hour, period = NA) %<-% parse_time("10:00 AM")
hour # "10:00"
period # "AM"
c(hour, period = NA) %<-% parse_time("15:00")
hour # "15:00"
period # NA
# right operator
list(1, 2, "a", "b", "c") %->% c(x, y, ...chars)
x # 1
y # 2
chars # list("a", "b", "c")
# magrittr chains, install.packages("magrittr") for this example
if (requireNamespace("magrittr", quietly = TRUE)) {
library(magrittr)
c("hello", "world!") %>%
paste0("\n") %>%
lapply(toupper) %->%
c(greeting, subject)
greeting # "HELLO\n"
subject # "WORLD!\n"
}Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.