The present invention relates to a computer-implemented method and a system for determining co-occurrences in at least one graph with n vertices and E edges, wherein each edge is defined by a pair of vertices, the method comprising: storing a binary adjacency matrix representing a first graph in a memory; performing a calculation step for the first graph, wherein the calculation step comprises: loading a block of at most K consecutive rows of the binary adjacency matrix from the memory and storing each row into one of K caches; streaming each of the subsequent uncached rows of the binary adjacency matrix from the memory; reading pairs of rows comprising a streamed row and each one of the cached rows; computing the logical conjunction between each couple of elements of the rows at the same position in the rows for each read pair of rows; and adding the results of the logical conjunction for all the couples of elements in each read pair by means of one-bit adders to obtain the co-occurrence, wherein the calculation step is repeated for consecutive blocks of rows in the binary adjacency matrix until all the pairs of rows of the binary adjacency matrix have been read.