Check if the Protein-Protein-interaction (PPI) has the expected format for this app
.checkPPI(ppi)a data.frame, Protein-protein interaction (PPI) network data
frame. The object is expected to have three columns, Gene1 and
Gene2 which specify the gene names of the interacting proteins
in no particular order (symmetric interaction) and a column
combined_score which is a numerical value of the strength of
the interaction.
A validated and formatted PPI data frame.