I see documentation for the nfilled function, but I don't seem to be able to access it. (Running version 0.3.0-prerelease+1174 (2014-01-23 16:58 UTC))
julia> S = sparse([2,3,4],[1,2,3],[4,5,6])
4x3 sparse matrix with 3 Int64 nonzeros:
[2, 1] = 4
[3, 2] = 5
[4, 3] = 6
julia> nfilled(S)
ERROR: nfilled not defined
