This function executes a ubuntu docker that create a sparse matrix, without 0s, from a dense one, including 0s
csvToSparse(group = c("sudo", "docker"), scratch.folder, file, separator)
a character string. Two options: sudo or docker, depending to which group the user belongs
a character string indicating the path of the scratch folder
a character string indicating the path of the file, with file name and extension included
separator used in count file, e.g. '\t', ','
three files: matrix.mtx, barcodes.tsv and genes.tsv