Fix issue with below limit strings in ngram calculation - #14685
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When strings provided were below `n` characters, the ngram function returns an empty list. This was previously exploded, without filtering out the empty lists, causing the <NA> token to occur erroneously. Now, the empty lists should be filtered out.
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/ok to test |
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/ok to test |
davidwendt
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Jan 11, 2024
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Just wondering if this fix is an appropriate, breaking change to cuDF behavior.
| result = self._return_or_inplace(lc, retain_index=True) | ||
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| if isinstance(result, cudf.Series) and not as_list: | ||
| result = result[result.list.len() > 0] # before exploding, removes those lists which have 0 length |
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Seems this fix could go in the calling code (cuml?).
Just pass as_list=True and do the filter step and explode outside this function.
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This fix should be included in the cuDF repo due to it being a bug in the character_ngrams function itself. sklearn does not have this underlying issue with the sklearn.feature_extraction.text.CountVectorizer class that causes NA tokens to be returned on empty strings for example.
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Ok. Could you add a pytest for this?
davidwendt
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Closing this in favor of #15371 |
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Fixes `character_ngrams` function to not include empty entries when `as_list=False`. That is, the exploded view (non-list result) should not contain empty or NA elements. This PR changes the `nvtext::generate_character_ngrams()` API to return a lists column instead of a flat strings column. The python code had been converting the return object into lists column and then exploding it if `as_list=False`. Returning as a list column simplifies the logic and prevents the double conversion. There is almost no impact to the nvtext code since the offsets for the output lists column were already being generated. All tests were updated to expect the new result. Also changed some exception types from `cudf::logic_error` to `std::invalid_argument` as appropriate. Continues work of abandoned PR #14685 Authors: - David Wendt (https://github.com/davidwendt) Approvers: - Bradley Dice (https://github.com/bdice) - Vyas Ramasubramani (https://github.com/vyasr) URL: #15371
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When strings provided were below
ncharacters, the ngram function returns an empty list. This was previously exploded, without filtering out the empty lists, causing the token to occur erroneously. Now, the empty lists should be filtered out.Description
Changes Proposed:
Should close the issue [BUG] #14684.
Addressed an issue in the ngram function where input strings below a specified length (n) resulted in the function returning an empty list. Previously, this empty list was not filtered out during further processing, leading to the inadvertent occurrence of the token.
Solution:
Modified the code to include a filtering step that removes empty lists generated by the ngram function when input strings are below the specified length. This ensures that the token is no longer erroneously introduced.
Impact:
This enhancement improves the accuracy and reliability of the ngram function by handling edge cases where input strings are shorter than the specified length. The filtering of empty lists prevents unintended consequences, specifically the occurrence of the token in such scenarios.
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