sparse matrixes, http://www.johnmyleswhite.com/notebook/2011/10/31/using-sparse-matrices-in-r/

sparse.r

library(Matrix)

## building a 729670 x 1167 object (fast enough)

M = list()

pb = txtProgressBar(min = 1, max = length(followers_m))

for(i in 1:length(followers_m)) {

  M[[i]] = as.numeric(userlist %in% followers_m[[i]])
  setTxtProgressBar(pb, i)

}

M = sapply(M, rbind)

## SIZE

# assembling took a few minutes
> dim(M)
[1] 729670   1167

> object.size(M) / 10^9
6.81219932 [G]bytes

# takes a few minutes
> M2 = Matrix(M)

> object.size(M2) / 10^9
0.1136096 [G]bytes

## NAMING

> system.time(colnames(M) <- gsub("followers/|\\.rda", "", filesList))
   user  system elapsed 
  7.274  20.754  38.679

> system.time(colnames(M2) <- gsub("followers/|\\.rda", "", filesList))
   user  system elapsed 
  0.004   0.000   0.005
  
## PRODUCT OF TRANSPOSE (two-mode to one-mode)

# takes forever if class(M) = matrix
> m = t(M) %*% M

> system.time(m <- t(M) %*% M)
   user  system elapsed 
  3.036   0.252   3.299
  
# oooh yeah
# improved network builder by HOURS