FEAT-#6498: Make Fold operator more flexible

[YarShev]

What do these changes do?

• first commit message and PR title follow format outlined here

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• passes flake8 modin/ asv_bench/benchmarks scripts/doc_checker.py
• passes black --check modin/ asv_bench/benchmarks scripts/doc_checker.py
• signed commit with git commit -s
• Resolves Does the Fold operator allow a function to change the shape of partitions? #6498
• tests passing
• module layout described at docs/development/architecture.rst is up-to-date

[anmyachev]

I feel that filter_modin_dataframe2 will not work. Could you double check?

Suggested change

	def filter_modin_dataframe(df):
	return df.__constructor__(
	query_compiler=df._query_compiler.filter_func(
	fold_axis=0,
	new_index=new_index,
	new_columns=new_columns,
	)
	)
	pd.DataFrame.filter_dataframe = filter_modin_dataframe
	filtered_df = modin_df.filter_dataframe()
	df_equals(filtered_df, expected_df)
	def filter_modin_dataframe1(df):
	return df.__constructor__(
	query_compiler=df._query_compiler.filter_func(
	fold_axis=0,
	new_index=new_index,
	new_columns=new_columns,
	)
	)
	pd.DataFrame.filter_dataframe1 = filter_modin_dataframe1
	filtered_df = modin_df.filter_dataframe1()
	df_equals(filtered_df, expected_df)
	def filter_modin_dataframe2(df):
	return df.__constructor__(
	query_compiler=df._query_compiler.filter_func(fold_axis=0)
	)
	pd.DataFrame.filter_dataframe2 = filter_modin_dataframe2
	filtered_df = modin_df.filter_dataframe2()
	df_equals(filtered_df, expected_df)

[YarShev]

It will not work since I assumed that if new_index/columns are not passed, then fold function must preserve the shape. Do you think we should add a note about that?

[anmyachev]

It seems that it is not always possible to know the index when the shape is saved. Let's add an additional flag that will say that the shape does not change. It will default to false so that users are less likely to get an error, on the other hand we can set this parameter to true for our functions that are already implemented through this operator. For example: shape_preserved: bool = False.

[YarShev]

Good suggestion! Done

[anmyachev]

@YarShev please resolve conflicts

[YarShev]

@YarShev please resolve conflicts

resolved