How can I get cocitation and bibliographic coupling similarity indices and then graphs, without using Biliometrix?

Hi,
I am trying to get cocitation and bibliographic coupling similarity indices (Jaccard, I guess) and then graphs, from a 2x8582 dataframe with citing and cited document IDs, using R. I haven't been able to use the Bibliometrix package, because the source is not WoS, Scopus, etc. With cocitation/bibcoupling from igraph I get huge matrices, so I guess I need to reduce the observations to the x most cited, but I don't know how to do that either. I also don't know how to calculate the similarity index once I have the matrix, because "similarity(g, method = "jaccard")" just gives me another matrix. Any help, please?