MegEngine/imperative/python/megengine/functional/metric.py

# -*- coding: utf-8 -*-
# MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
#
# Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
from typing import Iterable, Union

import numpy as np

from ..tensor import Tensor
from .math import topk as _topk
from .tensor import broadcast_to, transpose


def topk_accuracy(
    logits: Tensor, target: Tensor, topk: Union[int, Iterable[int]] = 1
) -> Union[Tensor, Iterable[Tensor]]:
    r"""
    Calculates the classification accuracy given predicted logits and ground-truth labels.

    :param logits: model predictions of shape `[batch_size, num_classes]`,
        representing the probability (likelyhood) of each class.
    :param target: ground-truth labels, 1d tensor of int32.
    :param topk: specifies the topk values, could be an int or tuple of ints. Default: 1
    :return: tensor(s) of classification accuracy between 0.0 and 1.0.

    Examples:

    .. testcode::

        import numpy as np
        from megengine import tensor
        import megengine.functional as F

        logits = tensor(np.arange(80, dtype=np.int32).reshape(8,10))
        target = tensor(np.arange(8, dtype=np.int32))
        top1, top5 = F.metric.topk_accuracy(logits, target, (1, 5))
        print(top1.numpy(), top5.numpy())

    Outputs:

    .. testoutput::

        0.0 0.375
    """
    if isinstance(topk, int):
        topk = (topk,)
    _, pred = _topk(logits, k=max(topk), descending=True)
    accs = []
    for k in topk:
        correct = pred[:, :k].detach() == broadcast_to(
            transpose(target, (0, "x")), (target.shape[0], k)
        )
        accs.append(correct.astype(np.float32).sum() / target.shape[0])
    if len(topk) == 1:  # type: ignore[arg-type]
        accs = accs[0]
    return accs