Use this if you are using igraph from R
Constructor modifier to drop multiple edges
without_multiples()
Other constructor modifiers: 
simplified(),
with_edge_(),
with_graph_(),
with_vertex_(),
without_attr(),
without_loops()
sample_(pa(10, m = 3, algorithm = "bag")) sample_(pa(10, m = 3, algorithm = "bag"), without_multiples())