![[Deprecated]](figures/lifecycle-deprecated.svg)
lift_xy() is a composition helper. It helps you compose
functions by lifting their domain from a kind of input to another
kind. The domain can be changed from and to a list (l), a vector
(v) and dots (d). For example, lift_ld(fun) transforms a
function taking a list to a function taking dots.
The most important of those helpers is probably lift_dl()
because it allows you to transform a regular function to one that
takes a list. This is often essential for composition with purrr
functional tools. Since this is such a common function,
lift() is provided as an alias for that operation.
These functions were superseded in purrr 1.0.0 because we no longer believe "lifting" to be a mainstream operation, and we are striving to reduce purrr to its most useful core. Superseded functions will not go away, but will only receive critical bug fixes.
Usage
lift(..f, ..., .unnamed = FALSE)
lift_dl(..f, ..., .unnamed = FALSE)
lift_dv(..f, ..., .unnamed = FALSE)
lift_vl(..f, ..., .type)
lift_vd(..f, ..., .type)
lift_ld(..f, ...)
lift_lv(..f, ...)Arguments
- ..f
A function to lift.
- ...
Default arguments for
..f. These will be evaluated only once, when the lifting factory is called.- .unnamed
If
TRUE,ldorlvwill not name the parameters in the lifted function signature. This prevents matching of arguments by name and match by position instead.- .type
Can be a vector mold specifying both the type and the length of the vectors to be concatenated, such as
numeric(1)orinteger(4). Alternatively, it can be a string describing the type, one of: "logical", "integer", "double", "complex", "character" or "raw".
from ... to list(...) or c(...)
Here dots should be taken here in a figurative way. The lifted
functions does not need to take dots per se. The function is
simply wrapped a function in do.call(), so instead
of taking multiple arguments, it takes a single named list or
vector which will be interpreted as its arguments. This is
particularly useful when you want to pass a row of a data frame
or a list to a function and don't want to manually pull it apart
in your function.
from c(...) to list(...) or ...
These factories allow a function taking a vector to take a list
or dots instead. The lifted function internally transforms its
inputs back to an atomic vector. purrr does not obey the usual R
casting rules (e.g., c(1, "2") produces a character
vector) and will produce an error if the types are not
compatible. Additionally, you can enforce a particular vector
type by supplying .type.
from list(...) to c(...) or ...
lift_ld() turns a function that takes a list into a
function that takes dots. lift_vd() does the same with a
function that takes an atomic vector. These factory functions are
the inverse operations of lift_dl() and lift_dv().
lift_vd() internally coerces the inputs of ..f to
an atomic vector. The details of this coercion can be controlled
with .type.
Examples
### Lifting from ... to list(...) or c(...)
x <- list(x = c(1:100, NA, 1000), na.rm = TRUE, trim = 0.9)
lift_dl(mean)(x)
#> [1] 51
# You can also use the lift() alias for this common operation:
lift(mean)(x)
#> [1] 51
# now:
exec(mean, !!!x)
#> [1] 51
# Default arguments can also be specified directly in lift_dl()
list(c(1:100, NA, 1000)) |> lift_dl(mean, na.rm = TRUE)()
#> [1] 59.90099
# now:
mean(c(1:100, NA, 1000), na.rm = TRUE)
#> [1] 59.90099
# lift_dl() and lift_ld() are inverse of each other.
# Here we transform sum() so that it takes a list
fun <- sum |> lift_dl()
fun(list(3, NA, 4, na.rm = TRUE))
#> [1] 7
# now:
fun <- function(x) exec("sum", !!!x)
exec(sum, 3, NA, 4, na.rm = TRUE)
#> [1] 7
### Lifting from c(...) to list(...) or ...
# In other situations we need the vector-valued function to take a
# variable number of arguments as with pmap(). This is a job for
# lift_vd():
pmap_dbl(mtcars, lift_vd(mean))
#> Warning: `lift_vd()` was deprecated in purrr 1.0.0.
#> [1] 29.90727 29.98136 23.59818 38.73955 53.66455 35.04909 59.72000
#> [8] 24.63455 27.23364 31.86000 31.78727 46.43091 46.50000 46.35000
#> [15] 66.23273 66.05855 65.97227 19.44091 17.74227 18.81409 24.88864
#> [22] 47.24091 46.00773 58.75273 57.37955 18.92864 24.77909 24.88027
#> [29] 60.97182 34.50818 63.15545 26.26273
# now
pmap_dbl(mtcars, \(...) mean(c(...)))
#> [1] 29.90727 29.98136 23.59818 38.73955 53.66455 35.04909 59.72000
#> [8] 24.63455 27.23364 31.86000 31.78727 46.43091 46.50000 46.35000
#> [15] 66.23273 66.05855 65.97227 19.44091 17.74227 18.81409 24.88864
#> [22] 47.24091 46.00773 58.75273 57.37955 18.92864 24.77909 24.88027
#> [29] 60.97182 34.50818 63.15545 26.26273
### Lifting from list(...) to c(...) or ...
# This kind of lifting is sometimes needed for function
# composition. An example would be to use pmap() with a function
# that takes a list. In the following, we use some() on each row of
# a data frame to check they each contain at least one element
# satisfying a condition:
mtcars |> pmap_lgl(lift_ld(some, partial(`<`, 200)))
#> Warning: `lift_ld()` was deprecated in purrr 1.0.0.
#> [1] FALSE FALSE FALSE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE
#> [12] TRUE TRUE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE TRUE
#> [23] TRUE TRUE TRUE FALSE FALSE FALSE TRUE FALSE TRUE FALSE
# now
mtcars |> pmap_lgl(\(...) any(c(...) > 200))
#> [1] FALSE FALSE FALSE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE
#> [12] TRUE TRUE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE TRUE
#> [23] TRUE TRUE TRUE FALSE FALSE FALSE TRUE FALSE TRUE FALSE