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joshidp opened this issue May 21, 2021 · 3 comments
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Getting error while calculating NDCG using sklearn #20119

joshidp opened this issue May 21, 2021 · 3 comments
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@joshidp
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joshidp commented May 21, 2021

I'm trying to calculate the NDCG score for binary relevance:

from sklearn import metrics

# test 1
y_true = [[3]]
y_score = [[5]]
metrics.ndcg_score(y_true, y_score)

And getting error

ValueError: Only ('multilabel-indicator', 'continuous-multioutput', 'multiclass-multioutput') formats are supported. Got binary instead

Below code snippet is working which has more than 1 item. Please suggest why single item array is not working.

from sklearn import metrics

# test 1
y_true = [[6 ,5, 4, 3, 2, 1]]
y_score = [[120, -2, -6, -3,  2, 12]]
metrics.ndcg_score(y_true, y_score)
@gfrisch
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gfrisch commented May 21, 2021

Not sure it is really a bug.
Trying to compute the ranking score of a single item list is a nonsense.
Should it obviously return 1 instead of an error ? Not sure ...

@joshidp
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joshidp commented May 21, 2021

It might not be a bug but during K Cross validation single item is being passed and causing failure, this behavior is not right and not well documented. Please help

@jeromedockes jeromedockes mentioned this issue Oct 18, 2021
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@glemaitre glemaitre added Bug and removed Bug: triage labels Dec 17, 2021
@glemaitre
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I am closing because this is a duplicate of #21335
Closing since the discussion is going on there

@mae5357 mae5357 mentioned this issue Sep 20, 2022
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@joshidp @glemaitre @gfrisch