Name of slot in '>MLZ_data from which to calculate
mean lengths, either: Len_df or Len_matrix. Only used if there are data in both slots.
sample.size
If TRUE, then the annual sample sizes will be calculated by
summing the cells in slot Len_matrix. Otherwise, sample sizes are set to 0 or 1
(whether mean lengths are calculated).
Value
An object of class '>MLZ_data to fill slots MeanLength, ss.