BUG: pandas.to_datetime reports incorrect index when failing. about pandas HOT 7 OPEN

Hi,
I noticed this issue and I'd like to help triage and potentially fix it. Is it okay if I proceed with investigating this bug?
Thanks!

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Sure! From the outside I would guess the series is processed in batches and accidentally the numeric index into the batch is returned instead of the index of the series element. If you play with the the length of the valid list you'll notice it jumping around but rarely being correct.

from pandas.

Thank you for the insight! I will look into this and investigate further, after I will update here. Appreciate the guidance!

from pandas.

Thanks for the report. It appears to me that duplicates are first removed from the values. It seems easiest to just remove the index from the error message. Further investigations and PRs to fix are welcome!

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Take

from pandas.

I'd like to work on this, thanks

from pandas.

Thanks for the report. It appears to me that duplicates are first removed from the values. It seems easiest to just remove the index from the error message. Further investigations and PRs to fix are welcome!

I took some time to look into the code and this seems correct.

The error message comes from:

array_strptime in pandas/pandas/_libs/tslibs/strptime.pyx

which appears to be called indirectly from pandas/pandas/core/tools/datetimes.py:1015

The cause appears to be as @rhshadrach said: the series is first deduplicated by _maybe_cache and only then the date-parsing is applied.

The branches at 1023 and 1029 appear to also be affected.

As a pandas.Series has an index it seems most consistent to me to report the item causing the error by the index.

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