Added access_row_tuples_by_indexs method

[Prakriti-nith]

#462
This PR aims to revert back the changes for access_row_tuples_by_indexs method.

[Shekharrajak]

I think, it will not work properly for dataframe having multi indexes. Can you please try with multi index and find the issue? We can have this method for dataframe having only index (not multi index).

[Shekharrajak]

Please also add testcases for dataframe having custom indexes like index: [:one, :two, :three, :four, :five])

[Prakriti-nith]

I tried it with multi indexes and found two different bugs which needs to be managed separately. This method will work with multi indexes only when a single multi-index is provided

1. I think there is a bug in #pos method of Daru::MultiIndex when multiple multi-indexes are provided. access_row_tuples_by_index will work in this case when the issue with pos method will be resolved.
   
   

2. #pos method is working fine in the below case but #access_row_tuples_by_indexs gives error as it uses index for creating new rows but the provided index is not actually the valid index. It is used to get the positions.
   

[Shekharrajak]

I think, the multi index issue must be handled in separate PR. This PR looks good. It would be better if you had added example along with above the method documentation.

[Shekharrajak]

Ping @zverok , @v0dro Please look into the PR as soon as possible.

Thanks!

[paisible-wanderer]

Note: in dataframe.rb, it is possible to use instead:

def access_row_tuples_by_indexs *indexes
  get_sub_dataframe(indexes, by_position: false).map_rows(&:to_a)
end

It is about 10 times slower that the current reverted code but, among the two bugs found by @Prakriti-nith , it is not affected by the second one (ie I have:

df.access_row_tuples_by_indexs [:a, :one]
=> [[11, 1], [12, 2]]

)

[Shekharrajak]

Thanks @paisible-wanderer for informing us. @Prakriti-nith , please use similar thing for dataframe having multi index and test it for different cases.