vec_chop {vctrs} | R Documentation |
vec_chop()
provides an efficient method to repeatedly slice a vector. It
captures the pattern of map(indices, vec_slice, x = x)
. When no indices
are supplied, it is generally equivalent to as.list()
.
vec_unchop()
combines a list of vectors into a single vector, placing
elements in the output according to the locations specified by indices
.
It is similar to vec_c()
, but gives greater control over how the elements
are combined. When no indices are supplied, it is identical to vec_c()
.
If indices
selects every value in x
exactly once, in any order, then
vec_unchop()
is the inverse of vec_chop()
and the following invariant
holds:
vec_unchop(vec_chop(x, indices), indices) == x
vec_chop(x, indices = NULL)
vec_unchop(
x,
indices = NULL,
ptype = NULL,
name_spec = NULL,
name_repair = c("minimal", "unique", "check_unique", "universal")
)
x |
A vector |
indices |
For For |
ptype |
If |
name_spec |
A name specification for combining
inner and outer names. This is relevant for inputs passed with a
name, when these inputs are themselves named, like
See the name specification topic. |
name_repair |
How to repair names, see |
vec_chop()
: A list of size vec_size(indices)
or, if indices == NULL
,
vec_size(x)
.
vec_unchop()
: A vector of type vec_ptype_common(!!!x)
, or ptype
, if
specified. The size is computed as vec_size_common(!!!indices)
unless
the indices are NULL
, in which case the size is vec_size_common(!!!x)
.
vec_chop()
vec_unchop()
vec_chop(1:5)
vec_chop(1:5, list(1, 1:2))
vec_chop(mtcars, list(1:3, 4:6))
# If `indices` selects every value in `x` exactly once,
# in any order, then `vec_unchop()` inverts `vec_chop()`
x <- c("a", "b", "c", "d")
indices <- list(2, c(3, 1), 4)
vec_chop(x, indices)
vec_unchop(vec_chop(x, indices), indices)
# When unchopping, size 1 elements of `x` are recycled
# to the size of the corresponding index
vec_unchop(list(1, 2:3), list(c(1, 3, 5), c(2, 4)))
# Names are retained, and outer names can be combined with inner
# names through the use of a `name_spec`
lst <- list(x = c(a = 1, b = 2), y = 1)
vec_unchop(lst, list(c(3, 2), c(1, 4)), name_spec = "{outer}_{inner}")
# An alternative implementation of `ave()` can be constructed using
# `vec_chop()` and `vec_unchop()` in combination with `vec_group_loc()`
ave2 <- function(.x, .by, .f, ...) {
indices <- vec_group_loc(.by)$loc
chopped <- vec_chop(.x, indices)
out <- lapply(chopped, .f, ...)
vec_unchop(out, indices)
}
breaks <- warpbreaks$breaks
wool <- warpbreaks$wool
ave2(breaks, wool, mean)
identical(
ave2(breaks, wool, mean),
ave(breaks, wool, FUN = mean)
)