I have a matrix of microarray (around 30000 genes X 800 samples) as a back-end data set. In the workflow, if someone input a gene of their interest, I need to find it's highly co-expressed genes based on back-end data set. For that, I need to calculate pairwise Pearson correlation of input gene against data set (in this case, 30000 pairs). I have tried psych package before and for this pairwise calculation, there might be some other better method. Also,I assume this process take a little long time. Can any experienced person can suggest on this?Thanks..