count item sequence &key from-end start end key test test-not → n

count-if predicate sequence &key from-end start end key → n

count-if-not predicate sequence &key from-end start end key → n

item — an object.

sequence — a proper sequence.

predicate — a designator for a function of one argument that returns a generalized boolean.

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 0 and nil, respectively.

key — a designator for a function of one argument, or nil.

n — a non-negative integer less than or equal to the length of sequence.

count, count-if, and count-if-not count and return the number of elements in the sequence bounded by start and end that satisfy the test.

The from-end has no direct effect on the result. However, if from-end is true, the elements of sequence will be supplied as arguments to the test, test-not, and key in reverse order, which may change the side-effects, if any, of those functions.

(count #\a "how many A's are there in here?") → 2 
(count-if-not #'oddp '((1) (2) (3) (4)) :key #'car) → 2 
(count-if #'upper-case-p "The Crying of Lot 49" :start 4) → 2

Should be prepared to signal an error of type type-error if sequence is not a proper sequence.

Section 17.2 (Rules about Test Functions), Section 3.6 (Traversal Rules and Side Effects)

The :test-not argument is deprecated.

The function count-if-not is deprecated.