list-access: List/vector access functions

In wwbrannon/schemeR: Ports of Lisp/Scheme Features to R

Description

These functions are accessors for various elements and subsequences of lists and vectors. They are written in a type-generic way and will work for any broadly defined sequence type: vectors, lists (aka "generic vectors") and pairlists.

Usage

car(x)

cdr(x)

first(x)

last(x)

caar(x)

cadr(x)

cdar(x)

cddr(x)

caaar(x)

caadr(x)

cadar(x)

caddr(x)

cdaar(x)

cdadr(x)

cddar(x)

cdddr(x)

caaaar(x)

caaadr(x)

caadar(x)

caaddr(x)

cadaar(x)

cadadr(x)

caddar(x)

cadddr(x)

cdaaar(x)

cdaadr(x)

cdadar(x)

cdaddr(x)

cddaar(x)

cddadr(x)

cdddar(x)

cddddr(x)

Arguments

x	The object whose elements or subsequences to access.

Details

Using "sequence" to mean list, other vector or pairlist, the basic functions here are

• car, which returns the first element of a sequence (car(x) is equivalent to x[[1]] for (pair)lists and to x[1] for vectors)

• cdr, which returns the sequence consisting of every element but the first, or NULL for a sequence of length 0 or length 1

• last, which returns the last element of a sequence

• first, which is an alias for car

There are also a large number of functions of the form cXXXXr, where there are two, three or four "a"'s or "d"'s between the c and r. These functions are compositions of car and cdr: to give one example, caadr(x) is equivalent to car(car(cdr(x))). All such functions with up to four letters between the c and the r are pre-defined here.

Value

A particular element or subsequence.

wwbrannon/schemeR documentation built on May 4, 2019, 12:03 p.m.