implement similar functions for polars

[samukweku]

in relation to #1343 - this is a list of functions missing in the polars library that could be implemented :

• clean_names
• pivot_longer
• pivot_wider
• xlsx_tables
• xlsx_cells
• read_commandline
• conditional_join
• complete
• expand_grid pl.join with how='cross' covers this
• convert_excel_date
• convert_matlab_date
• convert_unix_date pl.from_epoch covers this
• bin_numeric pl.Expr.cut covers this
• concatenate_columns can be replicated with pl.concat_str
• deconcatenate_columns pl.Expr.str.split covers this
• factorize_columns pl.rank(dense) or pl.Expr.to_physical covers this
• get_dupes Expr.is_duplicated() covers this
• jitter
• limit_column_characters
• min_max_scale
• move can be replicated with polars' selectors
• row_to_names
• shuffle pl.Expr.shuffle covers this
• sort_naturally
• take_first group_by.first() covers this
• also

Care should be taken to not create the function, if an existing solution already exists for any of these functions (probably named differently, or a combination of existing polars functions that covers all use cases of any of the listed functions above)

[samukweku]

the current pivot_longer implementation is not good enough. I'll submit a PR with improvements

[samukweku]

I assumed (wrongly) that polars' join maintains order (it only does so for left join). need to rethink the computation logic for complete. I'll submit a PR with improvements