Add ability for users to define which class is "positive" for label encoder in binary classification case - #3033
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@@ Coverage Diff @@
## main #3033 +/- ##
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- Coverage 99.8% 99.8% -0.0%
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Files 312 312
Lines 30184 30229 +45
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+ Hits 30095 30139 +44
- Misses 89 90 +1
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freddyaboulton
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freddyaboulton
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@angela97lin Thank you for picking up this issue! I think we can simplify the implementation if we just forgo the sklearn implementation and roll our own.
I think this will work:
def fit(self, X, y):
"""Fits the label encoder.
Args:
X (pd.DataFrame): The input training data of shape [n_samples, n_features]. Ignored.
y (pd.Series): The target training data of length [n_samples].
Returns:
self
Raises:
ValueError: If input `y` is None.
"""
if y is None:
raise ValueError("y cannot be None!")
y = infer_feature_types(y)
sorted_uniques = sorted(y.unique())
self.mapping = {val:i for i, val in enumerate(sorted_uniques)}
if self.parameters["positive_label"] is not None:
if len(self.mapping) != 2:
raise ValueError(
"positive_label should only be set for binary classification targets. Otherwise, positive_label should be None."
)
self.mapping = {val: int(val == self.parameters["positive_label"]) for val in sorted_uniques}
self.inverse_mapping = {val: i for i, val in self.mapping.items()}
return selfthe in transform and inverse_transform we just call map on the series with the right mapping.
Maybe there's a performance hit but we'll have to check.
| f"y contains previously unseen labels: {y_unique_values.difference(self.mapping.keys())}" | ||
| ) | ||
| y_t = y_ww.map(self.mapping) | ||
| return X, ww.init_series(y_t, logical_type="integer") |
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Without setting the logical type, we end up with a categorical column which defeats the purpose 😂
| proba = proba.iloc[:, 1] | ||
| if objective is None: | ||
| predictions = proba > self.threshold | ||
| predictions = predictions.astype(int) |
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This is necessary because it returns bools, which we don't know how to map back (since we expect ints!). Although we treated bools and 0/1 as interchangeable, it actually matters now that we're storing a mapping.
Previously with sklearn this wasn't an issue because they used np.searchsorted which would treat ints and bools the same. This is no longer true. :)
bchen1116
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bchen1116
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Nice! This looks good to me, solid test coverage!
freddyaboulton
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freddyaboulton
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Looks good to me @angela97lin ! Thank you
3 participants
Closes #2926.
General question: since we have specific behavior in the label encoder... should we just move away from using sklearn's and completely write our own? There isn't too much additional functionality we get from using sklearn's impl but we could end up with different stack traces depending on whether or not positive_label is defined (if defined, uses our stack traces and errors, if not, uses sklearn's).