The format is:
Formal class 'dgCMatrix' [package "Matrix"] with 6 slots
..@ i : int [1:249526] 1 2 4 8 9 11 13 15 18 20 ...
..@ p : int [1:501] 0 498 1014 1527 2048 2558 3036 3511 4035 4537 ...
..@ Dim : int [1:2] 1000 500
..@ Dimnames:List of 2
.. ..$ : NULL
.. ..$ : NULL
..@ x : num [1:249526] 1 1 1 1 1 1 1 1 1 1 ...
..@ factors : list()