r - Building and adjacency matrix -
    i wondering if guys can me building adjacency matrix. have data in cvs format this:   paper_id    author 2   foster-mcgregor, n. 3   van houte, m. 4   van de meerendonk, a. 5   farla, k. 6   van houte, m. 6   siegel, m. 8   farla, k. 11  farla, k. 11  verspagen, b.   as can see column "paper_id" has repeated value of 11, meaning "farla, k." , "verspagen, b." coauthors of publication. need build square weighted matrix using names of authors, counting times collaborating together.          does following looking for?   # simulate data. d <- data.frame(   id=c(2,3,4,5,6,6,8,11,11,12,12),   author=c("fn", "vm","va","fk","vm","sm","fk","fk","vb","fk","vb") )  d    id author 1   2     fn 2   3     vm 3   4     va 4   5     fk 5   6     vm 6   6     sm 7   8     fk 8  11     fk 9  11     vb 10 12     fk 11 12     vb  # create incidence matrix: m ...