[ASK] Question on ndcg_at_k calculation

[Lulu20220]

Description

Why are we using rank ('first) to get the order of the ideal ranking instead of rank('min') or rank('average)?

https://github.com/microsoft/recommenders/blob/main/recommenders/evaluation/python_evaluation.py#L687
line 597
df_idcg["irank"] = df_idcg.groupby(col_user, as_index=False, sort=False)[
col_rating
].rank("first", ascending=False)

In this case, if there is a tied in the rating, for example, item A, B, C, D, rating is 1, 0, 0,0. Using rank('first), irank = 1,2,3,4. But should we take the tied condition into consideration, that means the irank = 1,2,2,2?

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