# Copyright (C) 2021 Unitary Fund
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
from typing import Callable
from mitiq._typing import Bitstring, MeasurementResult
[docs]def post_select(
result: MeasurementResult,
selector: Callable[[Bitstring], bool],
inverted: bool = False,
) -> MeasurementResult:
"""Returns only the bitstrings which satisfy the predicate in ``selector``.
Args:
result: List of bitstrings.
selector: Predicate for which bitstrings to select. Examples:
* ``selector = lambda bitstring: sum(bitstring) == k``
- Select all bitstrings of Hamming weight ``k``.
* ``selector = lambda bitstring: sum(bitstring) <= k``
- Select all bitstrings of Hamming weight at most ``k``.
* ``selector = lambda bitstring: bitstring[0] == 1``
- Select all bitstrings such that the the first bit is 1.
inverted: Invert the selector predicate so that bitstrings which obey
``selector(bitstring) == False`` are selected and returned.
"""
return MeasurementResult(
[bits for bits in result.result if selector(bits) != inverted]
)