I think is good to know that list contain more than 600000 rows with around 14000 nodes (participants).
?read.table may be unreliable for large matrices and with 14/600 you'll end up with many NA's. You might do better with nbrs<- scan('nbrs.txt',skip=1,what=list('integer','integer',double(0))) names(nbrs) <- c('c1','c2','c3') xtabs(c3~c1+c2,nbrs,sparse=T) # returns 4 x 9 sparse Matrix of class "dgCMatrix" 1 2 3 4 5 6 7 8 9 1 . 0.065 0.044 . . . . . . 3 0.071 . . 0.016 0.011 . . . . 4 . . 0.004 . . . 0.004 . 0.004 5 . . . 0.010 . 0.011 . 0.009 0.004 Cheers ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.