Internal Function: Called within the metadata_map function.
Searches for previous OUTPUT files in the output_dir, that match the dataset
name.
If files exist, it removes duplicates and autos, and stores the rest of the
table variables in a dataframe.
Value
It returns a list of 2: df_prev_exist (a boolean) and df_prev (NULL or populated with table variables to copy)
See also
Other metadata_map_internal:
data_load(),
empty_count(),
empty_plot(),
end_plot(),
user_categorisation(),
user_categorisation_loop()
