keylist: Create a List With Unique Keys

In keylist: Lightweight List Extensions that Enforce Unique Keys

Create a List With Unique Keys

Description

Create a list with unique keys (either fully named, knlist, or a mix of named and unnamed, klist), erroring if duplicate keys are found.

Usage

keylist(..., .named = FALSE)

is.keylist(x)

as.keylist(x, ...)

## Default S3 method:
as.keylist(x, ..., .named = FALSE, .recursive = FALSE)

keylist.append(klst, values, after = length(klst))

Arguments

...	for keylist: objects, possibly named, for as.keylist: passed to other methods.
.named	boolean indicating whether the list should be fully named or not. If TRUE then all elements must be named and unique, if FALSE then names are not required but if they are present they must be unique.
x	object to be coerced or tested.
.recursive	boolean indicating whether to recursively validate nested lists. If TRUE then all nested lists will be validated and converted to keylists, if FALSE then only the top level list will be validated and converted to a keylist.
klst	passed to append: the keylist to which the values are to be appended.
values	passed to append: the values to be included in the modified keylist.
after	passed to append: a subscript, after which the values are to be appended.

Details

keylist() creates one of the two keylist objects: klist or knlist, depending on the value of the .named argument. Those methods are generally preferred as they are more explicit.

is.keylist() checks if an object inherits from either klist or knlist.

keylist.append() applies append to a keylist and validates the result depending on whether the input was a klist or knlist.

keylist objects accept any R object as elements, but the keys must be unique. The key validation is done at the top level, so nested lists are not validated unless they are also keylists. To recursively turn a nested list structure into keylists, use as.keylist(x, .recursive = TRUE) or one of the lower level variants.

Value

A list object of class klist or knlist. For is.keylist() a boolean.

Note

keylists compare names using C's strcmp function.

as.list and as.vector methods for keylist objects remove the class and return a base R list or vector.

See Also

klist and knlist.

Examples

keylist(a = 1, 2, b = 3) # default is a klist
try(keylist(1, a = 2, a = 1)) # duplicate keys not allowed

x <- keylist(a = 1, b = 2, .named = TRUE) # create a knlist
try(keylist(1, b = 2, .named = TRUE)) # unnamed keys not allowed
try(x[[1]] <- 1) # knlist only accepts character indexing for assignment

# objects within a keylist are not subject to validation
keylist(1, list(a = 1, a = 2))
try(keylist(1, keylist(a = 1, a = 2))) # but nested keylists are

# recursively validate and convert to keylist
x <- list(1, list(1, 2))
x <- as.keylist(x, .recursive = TRUE)
class(x[[2]]) # nested list is now a keylist

is.keylist(klist(1)) && is.keylist(knlist(a = 1)) # TRUE

keylist.append(klist(a = 1), list(2, b = 3)) # append to a klist
# c() method for keylist objects also validates
try(c(keylist(a = 1), list(a = 3)))

keylist documentation built on April 27, 2026, 5:11 p.m.