MemberQ

MemberQ[list,form]
returns True if an element of list matches form, and False otherwise.

MemberQ[list,form,levelspec]
tests all parts of list specified by levelspec.

MemberQ[form]
represents an operator form of MemberQ that can be applied to an expression.

Details and OptionsDetails and Options

  • form can be a pattern.
  • The first argument of MemberQ can have any head, not necessarily List.
  • MemberQ[list,form] immediately tests whether any expression in list matches form; Element[x,dom] asserts that x is an element of the symbolic domain dom.
  • MemberQ uses standard level specifications:
  • nlevels through n
    Infinitylevels through Infinity
    {n}level n only
    {n1,n2}levels through
  • The default value for levelspec in MemberQ is .
  • A positive level n consists of all parts of expr specified by n indices.
  • A negative level -n consists of all parts of expr with depth n.
  • Level consists of numbers, symbols, and other objects that do not have subparts.
  • Level corresponds to the whole expression.
  • With the option setting Heads->True, MemberQ looks at heads of expressions and their parts.
  • MemberQ works on associations, testing values but not keys.
  • MemberQ[form][expr] is equivalent to MemberQ[expr,form].
Introduced in 1988
(1.0)
| Updated in 1999
(4.0)