zl:1 - FTP

121 count-if
(count 'a '(a a b b a a) :start 1 :end 6) => 3
(count 'a #(a b b b a) ) => 2
For a table of related items: See the section "Searching for Sequence
I terns" in Symbolics Common Lisp: Language Concepts.
count Keyword For loop
count expr {into uar} {data-type}
If expr evaluates non-nil, a counter is incremented. The data-type defaults to
fixnum. When the epilogue of the loop is reached, uar has been set to the
accumulated result and can be used by the epilogue code.
I t is safe to reference the values in uar during the loop, but they should not be
modified until the epilogue code for the loop is reached.
The forms count and counting are synonymous.
Examples:
(defun num-entry (small-list)
(loop for x in small-list
count t into num
finally (return num») => NUN-ENTRY
(num-entry '(a b cd» => 4
I
Is equivalent to
(de fun num-entry (small-list)
(loop for x in small-list
counting t into num
finally (return num») => NUN-ENTRY
(num-entry '(a b cd» => 4
Not only can there be multiple accumulations in a loop, but a single accumulation
can come from multiple places within the same loop form, if the types of the
collections are compatible. count and sum are compatible.
See the section "loop Clauses", page 310.
count-if predicate sequence &key key from-end (start 0) end
Function
count-if returns a non-negative integer, which represents the number of
elements in the specified subsequence of sequence satisfying the predicate.
predicate is the test to be performed on each element.