Basic Examples

Find the duplicates in a list:
[◼]
DuplicatesList
[{x,y,x,z,y,w}]
In[]:=
{x,y}
Out[]=

Properties and Relations

DuplicatesList[list]
is equivalent to
Map

First
,
DeleteCases

Gather
[list],{_}
list=RandomInteger[20,100];
In[]:=
[◼]
DuplicatesList
[list]
In[]:=
{2,8,12,15,10,5,7,3,14,18,19,4,13,11,16,9,17,20,0}
Out[]=
Map[First,DeleteCases[Gather[list],{_}]]
In[]:=
{2,8,12,15,10,5,7,3,14,18,19,4,13,11,16,9,17,20,0}
Out[]=