cheapr (version 1.2.0)

list_lengths: 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_combine(..., .args = NULL)
list_drop_null(x)

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.

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.

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