sequence—a proper sequence.
from-end—a generalized boolean. The default is false.
test—a designator for a function of two arguments that returns a generalized boolean.
test-not—a designator for a function of two arguments that returns a generalized boolean.
start, end—bounding index designators of sequence.
The defaults for start and end are
key—a designator for a function of one argument,
remove-duplicates returns a modified copy of sequence
from which any element that matches another element occurring in
sequence has been removed.
If sequence is a vector, the result is a vector that has the same actual array element type as sequence. If sequence is a list, the result is a list.
delete-duplicates is like
delete-duplicates may modify sequence.
The elements of sequence are compared pairwise, and if any two match, then the one occurring earlier in sequence is discarded, unless from-end is true, in which case the one later in sequence is discarded.
return a sequence of the same type as
sequence with enough elements removed so that no two of the remaining
elements match. The order of the elements remaining in the result
is the same as the order in which they appear in sequence.
remove-duplicates returns a sequence
that may share
with sequence or may be identical to sequence
if no elements need to be removed.
delete-duplicates, when sequence is a list,
is permitted to
setf any part,
of the top-level list structure in that sequence.
When sequence is a vector,
is permitted to change the dimensions of the vector
and to slide its elements into new positions without
permuting them to produce the resulting vector.
(remove-duplicates "aBcDAbCd" :test #'char-equal :from-end t) → "aBcD" (remove-duplicates '(a b c b d d e)) → (A C B D E) (remove-duplicates '(a b c b d d e) :from-end t) → (A B C D E) (remove-duplicates '((foo #\a) (bar #\%) (baz #\A)) :test #'char-equal :key #'cadr) → ((BAR #\%) (BAZ #\A)) (remove-duplicates '((foo #\a) (bar #\%) (baz #\A)) :test #'char-equal :key #'cadr :from-end t) → ((FOO #\a) (BAR #\%)) (setq tester (list 0 1 2 3 4 5 6)) (delete-duplicates tester :key #'oddp :start 1 :end 6) → (0 4 5 6)
delete-duplicates might destructively modify sequence.
Should signal an error of type
type-error if sequence is not a proper sequence.
Section 3.2.1 (Compiler Terminology), Section 3.6 (Traversal Rules and Side Effects)
If sequence is a vector, the result might or might not be simple, and might or might not be identical to sequence.
The :test-not argument is deprecated.
These functions are useful for converting sequence into a canonical form suitable for representing a set.