#data: matrix of double or connection
serialize = function(data, file, type, nb_per_chunk)
{
	bin_data = file(file, "ab")
	#write data length on first call
	nbytes = ifelse(type=="double",8,4)
	first_write = FALSE
	if (file.info(file)$size == 0)
	{
		#number of items always on 8 bytes
		writeBin(0L, bin_data, size=8) #,endian="little")
		first_write = TRUE
	}
	if (is.matrix(data))
	{
		writeBin(t(data), bin_data, size=nbytes)
		data_length = ncol(data)
	}
	else #if (is(data, "connection"))
	{
		if (first_write)
		{
			data_line = scan(data, double(), sep=",", nlines=1)
			writeBin(data_line, bin_data, size=nbytes)
			data_length = length(data_line)
		}
		repeat
		{
			data_chunk = scan(data, double(), sep=",", nlines=nb_per_chunk)
			if (length(data_chunk)==0)
				break
			writeBin(data_chunk, bin_data, size=nbytes)
		}
	}
	if (first_write)
	{
		#ecrire file_size-1 / (nbytes*nbWritten) en 0 dans bin_data ! ignored == file_size
		ignored = seek(bin_data, 0)
		writeBin(data_length, bin_data, size=8)
	}
	close(bin_data)
}

#TODO: read in binary file, always same structure
getDataFromFile(indices, file, type)
{
	bin_data = file(file, "rb")
	nbytes = ifelse(type=="double",8,4)
	data_length = readBin(bin_data,"double",1,nbytes) #,endian="little")
	t(sapply(indices, function(i) readBin(bin_data,"double",n=data_length,size=nbytes)))
}