vctrs (version 0.7.0)

vec_chop: Chopping

Description

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().

Usage

vec_chop(x, ..., indices = NULL, sizes = NULL)

Value

A list where each element has the same type as x. The size of the list is equal to vec_size(indices), vec_size(sizes), or vec_size(x) depending on whether or not indices or sizes is provided.

Arguments

x

A vector

...

These dots are for future extensions and must be empty.

indices

A list of positive integer vectors to slice x with, or NULL. Can't be used if sizes is already specified. If both indices and sizes are NULL, x is split into its individual elements, equivalent to using an indices of as.list(vec_seq_along(x)).

sizes

An integer vector of non-negative sizes representing sequential indices to slice x with, or NULL. Can't be used if indices is already specified.

For example, sizes = c(2, 4) is equivalent to indices = list(1:2, 3:6), but is typically faster.

sum(sizes) must be equal to vec_size(x), i.e. sizes must completely partition x, but an individual size is allowed to be 0.

Dependencies

• vec_slice()

Examples

vec_chop(1:5)

# These two are equivalent
vec_chop(1:5, indices = list(1:2, 3:5))
vec_chop(1:5, sizes = c(2, 3))

# Can also be used on data frames
vec_chop(mtcars, indices = list(1:3, 4:6))

# If you know your input is sorted and you'd like to split on the groups,
# `vec_run_sizes()` can be efficiently combined with `sizes`
df <- data_frame(
  g = c(2, 5, 5, 6, 6, 6, 6, 8, 9, 9),
  x = 1:10
)
vec_chop(df, sizes = vec_run_sizes(df$g))

# If you have a list of homogeneous vectors, sometimes it can be useful to
# combine, apply a function to the flattened vector, and chop according
# to the original indices. This can be done efficiently with `list_sizes()`.
x <- list(c(1, 2, 1), c(3, 1), 5, double())
x_flat <- vec_c(!!!x)
x_flat <- x_flat + max(x_flat)
vec_chop(x_flat, sizes = list_sizes(x))