"""
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transforms.py is for shape-preserving functions.
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"""
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from __future__ import annotations
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import numpy as np
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from pandas._typing import AxisInt
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def shift(values: np.ndarray, periods: int, axis: AxisInt, fill_value) -> np.ndarray:
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new_values = values
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if periods == 0 or values.size == 0:
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return new_values.copy()
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# make sure array sent to np.roll is c_contiguous
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f_ordered = values.flags.f_contiguous
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if f_ordered:
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new_values = new_values.T
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axis = new_values.ndim - axis - 1
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if new_values.size:
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new_values = np.roll(
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new_values,
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np.intp(periods),
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axis=axis,
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)
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axis_indexer = [slice(None)] * values.ndim
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if periods > 0:
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axis_indexer[axis] = slice(None, periods)
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else:
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axis_indexer[axis] = slice(periods, None)
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new_values[tuple(axis_indexer)] = fill_value
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# restore original order
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if f_ordered:
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new_values = new_values.T
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return new_values
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