level parameter, loop either iterates through the list of ncdfFlowSet objects
or everyflowFrame objects.
"lapply"(X, FUN, level = 2, ...)ncdfFlowList objectfunction to applynumeric. It controls whether loop at `ncdfFlowSet` level or `sample` level.
when level = 2 (default value),FUN is applied to each sample. When level = 1, FUN is applied to each object stored in data slot.FUN