Wolfram: List. Check Exist

MemberQ

• MemberQ[ expr, pattern ]
• MemberQ[ expr, pattern, levelspec ] → limit to Level Spec.

Check existence by Pattern.

default Level Spec is {1}

• MemberQ

MemberQ[ {1, 2, 3}, 2 ]
(* True *)

MemberQ[ {1, {a, b}, 3}, {a, b} ]
(* True *)

(* using a pattern *)

MemberQ[ {1, {a, b}, 3}, {_, _} ]
(* True *)

MemberQ[ {1, {a, b}, 3}, _Integer ]
(* True *)

Count

• Count[ expr, pattern ]
• Count[ expr, pattern, levelspec ] → limit to Level Spec.

Count by Pattern

default Level Spec is {1}

• Count

Count[ {1, 2, 3, 1}, 1 ]
(* 2 *)

Count[ {1, {a, b}, 3}, {a, b} ]
(* 1 *)

(* using a pattern *)
Count[ {1, {a, b}, 3}, {_, _} ]
(* 1 *)

Count[ {1, {a, b}, 3}, _Integer ]
(* 2 *)

(* using a levelspec *)
Count[ {1,{2,{3,4}}}, {_, _} ]
(* 1 *)

Count[ {1,{2,{3,4}}}, {_, _}, {1,Infinity} ]
(* 2 *)