Uni-directional vs Bi-directional

        &  saddr   &  dport   &  sport   &    fsd   \\
\hline
 daddr&     0.135&     0.832&    -0.031&     0.217\\
 saddr&         -&    -0.012&     0.923&     0.268\\
 dport&         -&         -&    -0.210&     0.044\\
 sport&         -&         -&         -&     0.062\\