lists: List utilities

In cheapr: Simple Functions to Save Time and Memory

List utilities

Description

Functions to help work with lists.

Usage

list_lengths(x, names = FALSE)

lengths_(x, names = FALSE)

unlisted_length(x)

new_list(length = 0L, default = NULL)

list_assign(x, values)

list_modify(x, values)

list_combine(..., .args = NULL)

list_drop_null(x)

Arguments

x	A list.
names	Should names of list elements be added? Default is FALSE.
length	Length of list.
default	Default value for each list element.
values	A named list
...	Objects to combine into a list.
.args	An alternative to ... for easier programming with lists.

Value

list_lengths() returns the list lengths.
unlisted_length() is a fast alternative to length(unlist(x)).
new_list() is like vector("list", length) but also allows you to specify a default value for each list element. This can be useful for initialising with a catch-all value so that when you unlist you're guaranteed a list of length >= to the specified length.

list_assign() is vectorised version of ⁠[[<-⁠ that concatenates values to x or modifies x where the names match. Can be useful for modifying data frame variables.

list_combine() combines each element of a set of lists into a single list. If an element is not a list, it is treated as a length-one list. This happens to be very useful for combining data frame cols.

list_drop_null() removes NULL list elements very quickly.

Examples

library(cheapr)
l <- list(1:10,
          NULL,
          list(integer(), NA_integer_, 2:10))

lengths_(l) # Faster lengths()
unlisted_length(l) # length of vector if we unlist
paste0("length: ", length(print(unlist(l))))

unlisted_length(l) - na_count(l) # Number of non-NA elements

# We can create and initialise a new list with a default value
l <- new_list(20, 0L)
l[1:5]
# This works well with vctrs_list_of objects

cheapr documentation built on June 8, 2025, 11:35 a.m.