CLHS: Function COUNT, COUNT-IF, COUNT-IF-NOT

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Function COUNT, COUNT-IF, COUNT-IF-NOT

Syntax:

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

Arguments and Values:

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.

Description:

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.

Examples:

     (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

Side Effects: None.

Affected By: None.

Exceptional Situations:

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

See Also:

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

Notes:

The `:test-not` argument is deprecated.

The function count-if-not is deprecated.

The following X3J13 cleanup issues, not part of the specification, apply to this section:

- TEST-NOT-IF-NOT:FLUSH-ALL
- MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE
- RANGE-OF-START-AND-END-PARAMETERS:INTEGER-AND-INTEGER-NIL
- SUBSEQ-OUT-OF-BOUNDS

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