Add LogScaler transformer

rdt/transformers/__init__.py

@@ -28,6 +28,7 @@
     ClusterBasedNormalizer,
     FloatFormatter,
     GaussianNormalizer,
+    LogScaler,
 )
 from rdt.transformers.pii.anonymizer import (
     AnonymizedFaker,
@@ -46,6 +47,7 @@
     'FrequencyEncoder',
     'GaussianNormalizer',
     'LabelEncoder',
+    'LogScaler',
     'NullTransformer',
     'OneHotEncoder',
     'OptimizedTimestampEncoder',

rdt/transformers/numerical.py

@@ -8,7 +8,7 @@
 import pandas as pd
 import scipy
 
-from rdt.errors import TransformerInputError
+from rdt.errors import InvalidDataError, TransformerInputError
 from rdt.transformers.base import BaseTransformer
 from rdt.transformers.null import NullTransformer
 from rdt.transformers.utils import learn_rounding_digits
@@ -626,3 +626,122 @@
             recovered_data = np.stack([recovered_data, data[:, -1]], axis=1)  # noqa: PD013
 
         return super()._reverse_transform(recovered_data)
+
+
+class LogScaler(FloatFormatter):
+    """Transformer for numerical data using log.
+
+    This transformer scales numerical values using log and an optional constant.
+
+    Null values are replaced using a ``NullTransformer``.
+
+    Args:
+        missing_value_replacement (object):
+            Indicate what to replace the null values with. If an integer or float is given,
+            replace them with the given value. If the strings ``'mean'`` or ``'mode'``
+            are given, replace them with the corresponding aggregation and if ``'random'``
+            replace each null value with a random value in the data range. Defaults to ``mean``.
+        missing_value_generation (str or None):
+            The way missing values are being handled. There are three strategies:
+
+                * ``random``: Randomly generates missing values based on the percentage of
+                  missing values.
+                * ``from_column``: Creates a binary column that describes whether the original
+                  value was missing. Then use it to recreate missing values.
+                * ``None``: Do nothing with the missing values on the reverse transform. Simply
+                  pass whatever data we get through.
+         constant (float):
+            The constant to set as the 0-value for the log-based transform. Defaults to 0
+            (do not modify the 0-value of the data).
+        invert (bool):
+            Whether to invert the data with respect to the constant value. If False, do not
+            invert the data (all values will be greater than the constant value). If True,
+            invert the data (all the values will be less than the constant value).
+            Defaults to False.
+        learn_rounding_scheme (bool):
+            Whether or not to learn what place to round to based on the data seen during ``fit``.
+            If ``True``, the data returned by ``reverse_transform`` will be rounded to that place.
+            Defaults to ``False``.
+    """
+
+    def __init__(
+        self,
+        missing_value_replacement='mean',
+        missing_value_generation='random',
+        constant: float = 0.0,
+        invert: bool = False,
+        learn_rounding_scheme: bool = False,
+    ):
+        if isinstance(constant, float):
+            self.constant = constant
+        else:
+            raise ValueError('The constant parameter must be a float.')
+        if isinstance(invert, bool):
+            self.invert = invert
+        else:
+            raise ValueError('The invert parameter must be a bool.')
+
+        super().__init__(
+            missing_value_replacement=missing_value_replacement,
+            missing_value_generation=missing_value_generation,
+            learn_rounding_scheme=learn_rounding_scheme,
+        )
+
+    def _validate_data(self, data: pd.Series):
+        column_name = self.get_input_column()
+        if self.invert:
+            if not all(data < self.constant):
+                raise InvalidDataError(
+                    f"Unable to apply a log transform to column '{column_name}' due to constant"
+                    ' being too small.'
+                )
+        else:
+            if not all(data > self.constant):
+                raise InvalidDataError(
+                    f"Unable to apply a log transform to column '{column_name}' due to constant"
+                    ' being too large.'
+                )
+
+    def _fit(self, data):
+        super()._fit(data)
+        data = super()._transform(data)
+
+        if data.ndim > 1:
+            self._validate_data(data[:, 0])
+        else:
+            self._validate_data(data)
+
+    def _log_transform(self, data):
+        if self.invert:
+            return np.log(self.constant - data)
+        else:
+            return np.log(data - self.constant)
+
+    def _transform(self, data):
+        data = super()._transform(data)
+
+        if data.ndim > 1:
+            self._validate_data(data[:, 0])
+            data[:, 0] = self._log_transform(data[:, 0])
+        else:
+            self._validate_data(data)
+            data = self._log_transform(data)
+
+        return data
+
+    def _reverse_log(self, data):
+        if self.invert:
+            return self.constant - np.exp(data)
+        else:
+            return np.exp(data) + self.constant
+
+    def _reverse_transform(self, data):
+        if not isinstance(data, np.ndarray):
+            data = data.to_numpy()
+
+        if data.ndim > 1:
+            data[:, 0] = self._reverse_log(data[:, 0])
+        else:
+            data = self._reverse_log(data)
+
+        return super()._reverse_transform(data)

tests/integration/test_transformers.py

@@ -1,5 +1,6 @@
 from collections import defaultdict
 
+import numpy as np
 import pandas as pd
 import pytest
 
@@ -12,6 +13,8 @@
 
 PRIMARY_SDTYPES = ['boolean', 'categorical', 'datetime', 'numerical']
 
+INT64_MIN = np.iinfo(np.int64).min
+
 # Additional arguments for transformers
 TRANSFORMER_ARGS = {
     'BinaryEncoder': {
@@ -23,6 +26,7 @@
     'FloatFormatter': {'missing_value_generation': 'from_column'},
     'GaussianNormalizer': {'missing_value_generation': 'from_column'},
     'ClusterBasedNormalizer': {'missing_value_generation': 'from_column'},
+    'LogScaler': {'constant': float(INT64_MIN), 'missing_value_generation': 'from_column'},
 }
 
 # Mapping of rdt sdtype to dtype

tests/integration/transformers/test_numerical.py

@@ -7,6 +7,7 @@
     ClusterBasedNormalizer,
     FloatFormatter,
     GaussianNormalizer,
+    LogScaler,
 )
 
 
@@ -560,3 +561,61 @@ def test_out_of_bounds_reverse_transform(self):
 
         # Assert
         assert isinstance(reverse, pd.DataFrame)
+
+
+class TestLogScaler:
+    def test_learn_rounding(self):
+        """Test that transformer learns rounding scheme from data."""
+        # Setup
+        data = pd.DataFrame({'test': [1.0, np.nan, 1.5]})
+        transformer = LogScaler(
+            missing_value_generation=None,
+            missing_value_replacement='mean',
+            learn_rounding_scheme=True,
+        )
+        expected = pd.DataFrame({'test': [1.0, 1.2, 1.5]})
+
+        # Run
+        transformer.fit(data, 'test')
+        transformed = transformer.transform(data)
+        reversed = transformer.reverse_transform(transformed)
+
+        # Assert
+        np.testing.assert_array_equal(reversed, expected)
+
+    def test_missing_value_generation_from_column(self):
+        """Test from_column missing value generation with nans present."""
+        # Setup
+        data = pd.DataFrame({'test': [1.0, np.nan, 1.5]})
+        transformer = LogScaler(
+            missing_value_generation='from_column',
+            missing_value_replacement='mean',
+        )
+
+        # Run
+        transformer.fit(data, 'test')
+        transformed = transformer.transform(data)
+        reversed = transformer.reverse_transform(transformed)
+
+        # Assert
+        np.testing.assert_array_equal(reversed, data)
+
+    def test_missing_value_generation_random(self):
+        """Test random missing_value_generation with nans present."""
+        # Setup
+        data = pd.DataFrame({'test': [1.0, np.nan, 1.5, 1.5]})
+        transformer = LogScaler(
+            missing_value_generation='random',
+            missing_value_replacement='mode',
+            invert=True,
+            constant=3.0,
+        )
+        expected = pd.DataFrame({'test': [np.nan, 1.5, 1.5, 1.5]})
+
+        # Run
+        transformer.fit(data, 'test')
+        transformed = transformer.transform(data)
+        reversed = transformer.reverse_transform(transformed)
+
+        # Assert
+        np.testing.assert_array_equal(reversed, expected)