MemberQ

MemberQ[expr, pat] returns True if any of the elements in expr match pat, otherwise returns False.

Attributes[MemberQ] := {Protected}

Simple examples

In[1]:= MemberQ[{1, 2, 3}, 0]
Out[1]= False

In[2]:= MemberQ[{1, 2, 3}, 1]
Out[2]= True

In[3]:= MemberQ[{1, 2, 3}, {1}]
Out[3]= False

MemberQ works with patterns:

In[4]:= MemberQ[{1, 2, 3}, _Integer]
Out[4]= True

In[5]:= MemberQ[{1, 2, 3}, _]
Out[5]= True

In[6]:= MemberQ[{1, 2, 3}, _Real]
Out[6]= False

In[7]:= MemberQ[{1, 2, 3}, testmatch_Integer]
Out[7]= True

In[8]:= testmatch
Out[8]= testmatch

In[9]:= MemberQ[a, a]
Out[9]= False

In[10]:= MemberQ[a, _]
Out[10]= False

In[11]:= MemberQ[{a, b}, c]
Out[11]= False

In[12]:= MemberQ[{a, b}, a]
Out[12]= True

MemberQ works with BlankSequences:

In[1]:= MemberQ[{a, b}, ___]
Out[1]= True

In[2]:= MemberQ[{a, b}, __]
Out[2]= True

In[3]:= MemberQ[{a, b}, __Integer]
Out[3]= False

In[4]:= MemberQ[{a, b}, ___Integer]
Out[4]= False

In[5]:= MemberQ[{a, b}, ___Symbol]
Out[5]= True

In[6]:= MemberQ[{a, b}, __Symbol]
Out[6]= True

In[7]:= MemberQ[{a, b, 1}, __Symbol]
Out[7]= True

In[8]:= MemberQ[{a, b, 1}, __Integer]
Out[8]= True

expr need not be a List:

In[9]:= MemberQ[bar[a, b, c], a]
Out[9]= True

In[10]:= MemberQ[bar[a, b, c], bar]
Out[10]= False