Partial apply a function, filling in some arguments.
Partial function application allows you to modify a function by pre-filling some of the arguments. It is particularly useful in conjunction with functionals and other function operators.
Note that an argument can only be partialised once.
partial(.f, ..., .env = NULL, .lazy = NULL, .first = NULL)
.f |
a function. For the output source to read well, this should be a named function. |
... |
named arguments to Pass an empty These dots support quasiquotation and quosures. If you unquote a value, it is evaluated only once at function creation time. Otherwise, it is evaluated each time the function is called. |
.env |
Soft-deprecated as of purrr 0.3.0. The environments are now captured via quosures. |
.lazy |
Soft-deprecated as of purrr 0.3.0. Please unquote the arguments that should be evaluated once at function creation time. |
.first |
Soft-deprecated as of purrr 0.3.0. Please pass an
empty argument |
# Partial is designed to replace the use of anonymous functions for
# filling in function arguments. Instead of:
compact1 <- function(x) discard(x, is.null)
# we can write:
compact2 <- partial(discard, .p = is.null)
# partial() works fine with functions that do non-standard
# evaluation
my_long_variable <- 1:10
plot2 <- partial(plot, my_long_variable)
plot2()
plot2(runif(10), type = "l")
# Note that you currently can't partialise arguments multiple times:
my_mean <- partial(mean, na.rm = TRUE)
my_mean <- partial(my_mean, na.rm = FALSE)
try(my_mean(1:10))
# The evaluation of arguments normally occurs "lazily". Concretely,
# this means that arguments are repeatedly evaluated across invocations:
f <- partial(runif, n = rpois(1, 5))
f
f()
f()
# You can unquote an argument to fix it to a particular value.
# Unquoted arguments are evaluated only once when the function is created:
f <- partial(runif, n = !!rpois(1, 5))
f
f()
f()
# By default, partialised arguments are passed before new ones:
my_list <- partial(list, 1, 2)
my_list("foo")
# Control the position of these arguments by passing an empty
# `... = ` argument:
my_list <- partial(list, 1, ... = , 2)
my_list("foo")Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.