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 <- xtabs(~author+id,d) m       id author 2 3 4 5 6 8 11 12     fk 0 0 0 1 0 1  1  1     fn 1 0 0 0 0 0  0  0     sm 0 0 0 0 1 0  0  0     va 0 0 1 0 0 0  0  0     vb 0 0 0 0 0 0  1  1     vm 0 1 0 0 1 0  0  0  # convert adjacency matrix. # tcrossprod "m %*% t(m)" tcrossprod(m)       author author fk fn sm va vb vm     fk  4  0  0  0  2  0     fn  0  1  0  0  0  0     sm  0  0  1  0  0  1     va  0  0  0  1  0  0     vb  2  0  0  0  2  0     vm  0  0  1  0  0  2 

note crossprod() give incidence matrix id variable (i.e. t(m) %*% m).