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17.2.2 Satisfying a One-Argument Test

When using one of the functions in the next figure, the elements E of a sequence S are filtered not on the basis of the presence or absence of an object O under a two argument predicate, as with the functions described in Section 17.2.1 (Satisfying a Two-Argument Test), but rather on the basis of a one argument predicate.

assoc-if member-if rassoc-if
assoc-if-not member-if-not rassoc-if-not
count-if nsubst-if remove-if
count-if-not nsubst-if-not remove-if-not
delete-if nsubstitute-if subst-if
delete-if-not nsubstitute-if-not subst-if-not
find-if position-if substitute-if
find-if-not position-if-not substitute-if-not

Figure 17.3: Operators that have One-Argument Tests to be Satisfied

The element Ei might not be considered directly. If a :key argument is provided, it is a designator for a function of one argument to be called with each Ei as an argument, and yielding an object Zi to be used for comparison. (If there is no :key argument, Zi is Ei.)

Functions defined in this specification and having a name that ends in “-if” accept a first argument that is a designator for a function of one argument, Zi. An Ei is said to satisfy the test if this :test function returns a generalized boolean representing true.

Functions defined in this specification and having a name that ends in “-if-not” accept a first argument that is a designator for a function of one argument, Zi. An Ei is said to satisfy the test if this :test function returns a generalized boolean representing false.

17.2.2.1 Examples of Satisfying a One-Argument Test
 (count-if #'zerop '(1 #C(0.0 0.0) 0 0.0d0 0.0s0 3)) → 4

 (remove-if-not #'symbolp '(0 1 2 3 4 5 6 7 8 9 A B C D E F))
→ (A B C D E F)
 (remove-if (complement #'symbolp) '(0 1 2 3 4 5 6 7 8 9 A B C D E F))
→ (A B C D E F)

 (count-if #'zerop '("foo" "" "bar" "" "" "baz" "quux") :key #'length)
→ 3