Syntax: @dupselem(A1[, A2,...])
Argument 1: vector or matrix, A1
Argument 2+: (optional) vector or matrix, A2,...
Return: vector
Returns a vector of element IDs enumerating the observations within a duplicate group, as determined by @dupsid. The element IDs for any two observations with the same group ID are distinct.
See also
@dupsobs and
@dupsid.