metric.py

import logging
from typing import Any, Callable, Optional

import numpy as np
from numpy.typing import ArrayLike

logger = logging.getLogger(__name__)


def threshold_predictions(y: np.ndarray,
                          threshold: Optional[float] = None) -> np.ndarray:
    """Threshold predictions from classification model.

    Parameters
    ----------
    y: np.ndarray
        Must have shape `(N, n_classes)` and be class probabilities.
    threshold: float, default None
        The threshold probability for the positive class. Note that this
        threshold will only be applied for binary classifiers (where
        `n_classes==2`). If specified for multiclass problems, or if
        `threshold` is None, the threshold is ignored and argmax(y) is
        returned.

    Returns
    -------
    y_out: np.ndarray
        A numpy array of shape `(N,)` with class predictions as integers ranging from 0
        to `n_classes-1`.
    """
    if not isinstance(y, np.ndarray) or not len(y.shape) == 2:
        raise ValueError("y must be a ndarray of shape (N, n_classes)")
    N = y.shape[0]
    n_classes = y.shape[1]
    if n_classes != 2 or threshold is None:
        return np.argmax(y, axis=1)
    else:
        return np.where(y[:, 1] >= threshold, np.ones(N), np.zeros(N))


def normalize_weight_shape(w: Optional[np.ndarray], n_samples: int,
                           n_tasks: int) -> np.ndarray:
    """A utility function to correct the shape of the weight array.

    This utility function is used to normalize the shapes of a given
    weight array.

    Parameters
    ----------
    w: np.ndarray
        `w` can be `None` or a scalar or a `np.ndarray` of shape
        `(n_samples,)` or of shape `(n_samples, n_tasks)`. If `w` is a
        scalar, it's assumed to be the same weight for all samples/tasks.
    n_samples: int
        The number of samples in the dataset. If `w` is not None, we should
        have `n_samples = w.shape[0]` if `w` is a ndarray
    n_tasks: int
        The number of tasks. If `w` is 2d ndarray, then we should have
        `w.shape[1] == n_tasks`.

    Examples
    --------
    >>> import numpy as np
    >>> w_out = normalize_weight_shape(None, n_samples=10, n_tasks=1)
    >>> (w_out == np.ones((10, 1))).all()
    True

    Returns
    -------
    w_out: np.ndarray
        Array of shape `(n_samples, n_tasks)`
    """
    if w is None:
        w_out = np.ones((n_samples, n_tasks))
    elif isinstance(w, np.ndarray):
        if len(w.shape) == 0:
            # scalar case
            w_out = w * np.ones((n_samples, n_tasks))
        elif len(w.shape) == 1:
            if len(w) != n_samples:
                raise ValueError("Length of w isn't n_samples")
            # per-example case
            # This is a little arcane but it repeats w across tasks.
            w_out = np.tile(w, (n_tasks, 1)).T
        elif len(w.shape) == 2:
            if w.shape == (n_samples, 1):
                # If w.shape == (n_samples, 1) handle it as 1D
                w = np.squeeze(w, axis=1)
                w_out = np.tile(w, (n_tasks, 1)).T
            elif w.shape != (n_samples, n_tasks):
                raise ValueError(
                    "Shape for w doens't match (n_samples, n_tasks)")
            else:
                # w.shape == (n_samples, n_tasks)
                w_out = w
        else:
            raise ValueError("w must be of dimension 1, 2, or 3")
    else:
        # scalar case
        w_out = w * np.ones((n_samples, n_tasks))
    return w_out


def normalize_labels_shape(y: np.ndarray,
                           mode: Optional[str] = None,
                           n_tasks: Optional[int] = None,
                           n_classes: Optional[int] = None) -> np.ndarray:
    """A utility function to correct the shape of the labels.

    Parameters
    ----------
    y: np.ndarray
        `y` is an array of shape `(N,)` or `(N, n_tasks)` or `(N, n_tasks, 1)`.
    mode: str, default None
        If `mode` is "classification" or "regression", attempts to apply
        data transformations.
    n_tasks: int, default None
        The number of tasks this class is expected to handle.
    n_classes: int, default None
        If specified use this as the number of classes. Else will try to
        impute it as `n_classes = max(y) + 1` for arrays and as
        `n_classes=2` for the case of scalars. Note this parameter only
        has value if `mode=="classification"`

    Returns
    -------
    y_out: np.ndarray
        If `mode=="classification"`, `y_out` is an array of shape `(N,
        n_tasks, n_classes)`. If `mode=="regression"`, `y_out` is an array
        of shape `(N, n_tasks)`.
    """
    if n_tasks is None:
        raise ValueError("n_tasks must be specified")
    if mode not in ["classification", "regression"]:
        raise ValueError("mode must be either classification or regression.")
    if mode == "classification" and n_classes is None:
        raise ValueError("n_classes must be specified")
    if not isinstance(y, np.ndarray):
        raise ValueError("y must be a np.ndarray")
    # Handle n_classes/n_task shape ambiguity
    if mode == "classification" and len(y.shape) == 2:
        if n_classes == y.shape[1] and n_tasks != 1 and n_classes != n_tasks:
            raise ValueError("Shape of input doesn't match expected n_tasks=1")
        elif n_classes == y.shape[1] and n_tasks == 1:
            # Add in task dimension
            y = np.expand_dims(y, 1)
    if len(y.shape) == 1 and n_tasks != 1:
        raise ValueError("n_tasks must equal 1 for a 1D set of labels.")
    if (len(y.shape) == 2 or len(y.shape) == 3) and n_tasks != y.shape[1]:
        raise ValueError("Shape of input doesn't match expected n_tasks=%d" %
                         n_tasks)
    if len(y.shape) >= 4:
        raise ValueError(
            "Labels y must be a float scalar or a ndarray of shape `(N,)` or "
            "`(N, n_tasks)` or `(N, n_tasks, 1)` for regression problems and "
            "of shape `(N,)` or `(N, n_tasks)` or `(N, n_tasks, 1)` for classification problems"
        )
    if len(y.shape) == 1:
        # Insert a task dimension (we know n_tasks=1 from above0
        y_out = np.expand_dims(y, 1)
    elif len(y.shape) == 2:
        y_out = y
    elif len(y.shape) == 3:
        # If 3D and last dimension isn't 1, assume this is one-hot encoded and return as-is.
        if y.shape[-1] != 1:
            return y
        y_out = np.squeeze(y, axis=-1)
    # Handle classification. We need to convert labels into one-hot representation.
    if mode == "classification":
        all_y_task = []
        for task in range(n_tasks):
            y_task = y_out[:, task]
            # check whether n_classes is int or not
            assert isinstance(n_classes, int)
            y_hot = to_one_hot(y_task, n_classes=n_classes)
            y_hot = np.expand_dims(y_hot, 1)
            all_y_task.append(y_hot)
        y_out = np.concatenate(all_y_task, axis=1)
    return y_out


def normalize_prediction_shape(y: np.ndarray,
                               mode: Optional[str] = None,
                               n_tasks: Optional[int] = None,
                               n_classes: Optional[int] = None):
    """A utility function to correct the shape of provided predictions.

    The metric computation classes expect that inputs for classification
    have the uniform shape `(N, n_tasks, n_classes)` and inputs for
    regression have the uniform shape `(N, n_tasks)`. This function
    normalizes the provided input array to have the desired shape.

    Examples
    --------
    >>> import numpy as np
    >>> y = np.random.rand(10)
    >>> y_out = normalize_prediction_shape(y, "regression", n_tasks=1)
    >>> y_out.shape
    (10, 1)

    Parameters
    ----------
    y: np.ndarray
        If `mode=="classification"`, `y` is an array of shape `(N,)` or
        `(N, n_tasks)` or `(N, n_tasks, n_classes)`. If
        `mode=="regression"`, `y` is an array of shape `(N,)` or `(N,
        n_tasks)`or `(N, n_tasks, 1)`.
    mode: str, default None
        If `mode` is "classification" or "regression", attempts to apply
        data transformations.
    n_tasks: int, default None
        The number of tasks this class is expected to handle.
    n_classes: int, default None
        If specified use this as the number of classes. Else will try to
        impute it as `n_classes = max(y) + 1` for arrays and as
        `n_classes=2` for the case of scalars. Note this parameter only
        has value if `mode=="classification"`

    Returns
    -------
    y_out: np.ndarray
      If `mode=="classification"`, `y_out` is an array of shape `(N,
      n_tasks, n_classes)`. If `mode=="regression"`, `y_out` is an array
      of shape `(N, n_tasks)`.
    """
    if n_tasks is None:
        raise ValueError("n_tasks must be specified")
    if mode == "classification" and n_classes is None:
        raise ValueError("n_classes must be specified")
    if not isinstance(y, np.ndarray):
        raise ValueError("y must be a np.ndarray")
    # Handle n_classes/n_task shape ambiguity
    if mode == "classification" and len(y.shape) == 2:
        if n_classes == y.shape[1] and n_tasks != 1 and n_classes != n_tasks:
            raise ValueError("Shape of input doesn't match expected n_tasks=1")
        elif n_classes == y.shape[1] and n_tasks == 1:
            # Add in task dimension
            y = np.expand_dims(y, 1)
    if (len(y.shape) == 2 or len(y.shape) == 3) and n_tasks != y.shape[1]:
        raise ValueError("Shape of input doesn't match expected n_tasks=%d" %
                         n_tasks)
    if len(y.shape) >= 4:
        raise ValueError(
            "Predictions y must be a float scalar or a ndarray of shape `(N,)` or "
            "`(N, n_tasks)` or `(N, n_tasks, 1)` for regression problems and "
            "of shape `(N,)` or `(N, n_tasks)` or `(N, n_tasks, n_classes)` for classification problems"
        )
    if mode == "classification":
        if n_classes is None:
            raise ValueError("n_classes must be specified.")
        if len(y.shape) == 1 or len(y.shape) == 2:
            # Make everything 2D so easy to handle
            if len(y.shape) == 1:
                y = y[:, np.newaxis]
            # Handle each task separately.
            all_y_task = []
            for task in range(n_tasks):
                y_task = y[:, task]
                if len(np.unique(y_task)) > n_classes:
                    # Handle continuous class probabilites of positive class for binary
                    if n_classes > 2:
                        raise ValueError(
                            "Cannot handle continuous probabilities for multiclass problems."
                            "Need a per-class probability")
                    # Fill in class 0 probabilities
                    y_task = np.array([1 - y_task, y_task]).T
                    # Add a task dimension to concatenate on
                    y_task = np.expand_dims(y_task, 1)
                    all_y_task.append(y_task)
                else:
                    # Handle binary labels
                    # make y_hot of shape (N, n_classes)
                    y_task = to_one_hot(y_task, n_classes=n_classes)
                    # Add a task dimension to concatenate on
                    y_task = np.expand_dims(y_task, 1)
                    all_y_task.append(y_task)
            y_out = np.concatenate(all_y_task, axis=1)
        elif len(y.shape) == 3:
            y_out = y
    elif mode == "regression":
        if len(y.shape) == 1:
            # Insert a task dimension
            y_out = np.expand_dims(y, 1)
        elif len(y.shape) == 2:
            y_out = y
        elif len(y.shape) == 3:
            if y.shape[-1] != 1:
                raise ValueError(
                    "y must be a float scalar or a ndarray of shape `(N,)` or "
                    "`(N, n_tasks)` or `(N, n_tasks, 1)` for regression problems."
                )
            y_out = np.squeeze(y, axis=-1)
    else:
        raise ValueError("mode must be either classification or regression.")
    return y_out


def handle_classification_mode(
        y: np.ndarray,
        classification_handling_mode: Optional[str],
        threshold_value: Optional[float] = None) -> np.ndarray:
    """Handle classification mode.

    Transform predictions so that they have the correct classification mode.

    Parameters
    ----------
    y: np.ndarray
        Must be of shape `(N, n_tasks, n_classes)`
    classification_handling_mode: str, default None
        DeepChem models by default predict class probabilities for
        classification problems. This means that for a given singletask
        prediction, after shape normalization, the DeepChem prediction will be a
        numpy array of shape `(N, n_classes)` with class probabilities.
        `classification_handling_mode` is a string that instructs this method
        how to handle transforming these probabilities. It can take on the
        following values:
        - None: default value. Pass in `y_pred` directy into `self.metric`.
        - "threshold": Use `threshold_predictions` to threshold `y_pred`. Use
          `threshold_value` as the desired threshold.
        - "threshold-one-hot": Use `threshold_predictions` to threshold `y_pred`
          using `threshold_values`, then apply `to_one_hot` to output.
    threshold_value: float, default None
        If set, and `classification_handling_mode` is "threshold" or
        "threshold-one-hot" apply a thresholding operation to values with this
        threshold. This option isj only sensible on binary classification tasks.
        If float, this will be applied as a binary classification value.

    Returns
    -------
    y_out: np.ndarray
        If `classification_handling_mode` is "direct", then of shape `(N, n_tasks, n_classes)`.
        If `classification_handling_mode` is "threshold", then of shape `(N, n_tasks)`.
        If `classification_handling_mode is "threshold-one-hot", then of shape `(N, n_tasks, n_classes)"
    """
    if len(y.shape) != 3:
        raise ValueError("y must be of shape (N, n_tasks, n_classes)")
    N, n_tasks, n_classes = y.shape
    if classification_handling_mode == "direct":
        return y
    elif classification_handling_mode == "threshold":
        thresholded = []
        for task in range(n_tasks):
            task_array = y[:, task, :]
            # Now of shape (N,)
            task_array = threshold_predictions(task_array, threshold_value)
            # Now of shape (N, 1)
            task_array = np.expand_dims(task_array, 1)
            thresholded.append(task_array)
        # Returns shape (N, n_tasks)
        return np.concatenate(thresholded, axis=1)
    elif classification_handling_mode == "threshold-one-hot":
        thresholded = []
        for task in range(n_tasks):
            task_array = y[:, task, :]
            # Now of shape (N,)
            task_array = threshold_predictions(task_array, threshold_value)
            # Now of shape (N, n_classes)
            task_array = to_one_hot(task_array, n_classes=n_classes)
            # Now of shape (N, 1, n_classes)
            task_array = np.expand_dims(task_array, 1)
            thresholded.append(task_array)
        # Returns shape (N, n_tasks, n_classes)
        return np.concatenate(thresholded, axis=1)
    else:
        raise ValueError(
            "classification_handling_mode must be one of direct, threshold, threshold-one-hot"
        )


def to_one_hot(y: np.ndarray, n_classes: int = 2) -> np.ndarray:
    """Transforms label vector into one-hot encoding.

    Turns y into vector of shape `(N, n_classes)` with a one-hot
    encoding. Assumes that `y` takes values from `0` to `n_classes - 1`.

    Parameters
    ----------
    y: np.ndarray
        A vector of shape `(N,)` or `(N, 1)`
    n_classes: int, default 2
        If specified use this as the number of classes. Else will try to
        impute it as `n_classes = max(y) + 1` for arrays and as
        `n_classes=2` for the case of scalars. Note this parameter only
        has value if `mode=="classification"`

    Returns
    -------
    np.ndarray
        A numpy array of shape `(N, n_classes)`.
    """
    if len(y.shape) > 2:
        raise ValueError("y must be a vector of shape (N,) or (N, 1)")
    if len(y.shape) == 2 and y.shape[1] != 1:
        raise ValueError("y must be a vector of shape (N,) or (N, 1)")
    if len(np.unique(y)) > n_classes:
        raise ValueError("y has more than n_class unique elements.")
    N = np.shape(y)[0]
    y_hot = np.zeros((N, n_classes))
    y_hot[np.arange(N), y.astype(np.int64)] = 1
    return y_hot


def from_one_hot(y: np.ndarray, axis: int = 1) -> np.ndarray:
    """Transforms label vector from one-hot encoding.

    Parameters
    ----------
    y: np.ndarray
        A vector of shape `(n_samples, num_classes)`
    axis: int, optional (default 1)
        The axis with one-hot encodings to reduce on.

    Returns
    -------
    np.ndarray
        A numpy array of shape `(n_samples,)`
    """
    return np.argmax(y, axis=axis)


class Metric(object):
    """Wrapper class for computing user-defined metrics.

    The `Metric` class provides a wrapper for standardizing the API
    around different classes of metrics that may be useful for DeepChem
    models. The implementation provides a few non-standard conveniences
    such as built-in support for multitask and multiclass metrics.

    There are a variety of different metrics this class aims to support.
    Metrics for classification and regression that assume that values to
    compare are scalars are supported.

    At present, this class doesn't support metric computation on models
    which don't present scalar outputs. For example, if you have a
    generative model which predicts images or molecules, you will need
    to write a custom evaluation and metric setup.
    """

    def __init__(self,
                 metric: Callable[..., float],
                 task_averager: Optional[Callable[..., Any]] = None,
                 name: Optional[str] = None,
                 threshold: Optional[float] = None,
                 mode: Optional[str] = None,
                 n_tasks: Optional[int] = None,
                 classification_handling_mode: Optional[str] = None,
                 threshold_value: Optional[float] = None):
        """
        Parameters
        ----------
        metric: function
            Function that takes args y_true, y_pred (in that order) and
            computes desired score. If sample weights are to be considered,
            `metric` may take in an additional keyword argument
            `sample_weight`.
        task_averager: function, default None
            If not None, should be a function that averages metrics across
            tasks.
        name: str, default None
            Name of this metric
        threshold: float, default None (DEPRECATED)
            Used for binary metrics and is the threshold for the positive
            class.
        mode: str, default None
            Should usually be "classification" or "regression."
        n_tasks: int, default None
            The number of tasks this class is expected to handle.
        classification_handling_mode: str, default None
            DeepChem models by default predict class probabilities for
            classification problems. This means that for a given singletask
            prediction, after shape normalization, the DeepChem labels and prediction will be
            numpy arrays of shape `(n_samples, n_tasks, n_classes)` with class probabilities.
            `classification_handling_mode` is a string that instructs this method
            how to handle transforming these probabilities. It can take on the
            following values:
            - "direct": Pass `y_true` and `y_pred` directy into `self.metric`.
            - "threshold": Use `threshold_predictions` to threshold `y_true` and `y_pred`.
              Use `threshold_value` as the desired threshold. This converts them into
              arrays of shape `(n_samples, n_tasks)`, where each element is a class index.
            - "threshold-one-hot": Use `threshold_predictions` to threshold `y_true` and `y_pred`
              using `threshold_values`, then apply `to_one_hot` to output.
            - None: Select a mode automatically based on the metric.
        threshold_value: float, default None
            If set, and `classification_handling_mode` is "threshold" or
            "threshold-one-hot", apply a thresholding operation to values with this
            threshold. This option is only sensible on binary classification tasks.
            For multiclass problems, or if `threshold_value` is None, argmax() is used
            to select the highest probability class for each task.
        """
        if threshold is not None:
            logger.warn(
                "threshold is deprecated and will be removed in a future version of DeepChem."
                "Set threshold in compute_metric instead.")

        self.metric = metric
        if task_averager is None:
            self.task_averager = np.mean
        else:
            self.task_averager = task_averager
        if name is None:
            if task_averager is None:
                if hasattr(self.metric, '__name__'):
                    self.name = self.metric.__name__
                else:
                    self.name = "unknown metric"
            else:
                if hasattr(self.metric, '__name__'):
                    self.name = task_averager.__name__ + "-" + self.metric.__name__
                else:
                    self.name = "unknown metric"
        else:
            self.name = name

        if mode is None:
            # These are some smart defaults
            if self.metric.__name__ in [
                    "roc_auc_score", "matthews_corrcoef", "recall_score",
                    "accuracy_score", "kappa_score", "cohen_kappa_score",
                    "precision_score", "precision_recall_curve",
                    "balanced_accuracy_score", "prc_auc_score", "f1_score",
                    "bedroc_score", "jaccard_score", "jaccard_index",
                    "pixel_error"
            ]:
                mode = "classification"
            elif self.metric.__name__ in [
                    "pearson_r2_score", "r2_score", "mean_squared_error",
                    "mean_absolute_error", "rms_score", "mae_score", "pearsonr",
                    "concordance_index"
            ]:
                mode = "regression"
            else:
                raise ValueError(
                    "Please specify the mode of this metric. mode must be 'regression' or 'classification'"
                )
        if mode == "classification":
            if classification_handling_mode is None:
                # These are some smart defaults corresponding to sklearn's required
                # behavior
                if self.metric.__name__ in [
                        "matthews_corrcoef", "cohen_kappa_score", "kappa_score",
                        "balanced_accuracy_score", "recall_score",
                        "jaccard_score", "jaccard_index", "pixel_error",
                        "f1_score"
                ]:
                    classification_handling_mode = "threshold"
                elif self.metric.__name__ in [
                        "accuracy_score", "precision_score", "bedroc_score"
                ]:
                    classification_handling_mode = "threshold-one-hot"
                elif self.metric.__name__ in [
                        "roc_auc_score", "prc_auc_score",
                        "precision_recall_curve"
                ]:
                    classification_handling_mode = "direct"
            if classification_handling_mode not in [
                    "direct", "threshold", "threshold-one-hot"
            ]:
                raise ValueError(
                    "classification_handling_mode must be one of 'direct', 'threshold', 'threshold_one_hot'"
                )

        self.mode = mode
        self.n_tasks = n_tasks
        self.classification_handling_mode = classification_handling_mode
        self.threshold_value = threshold_value

    def compute_metric(self,
                       y_true: ArrayLike,
                       y_pred: ArrayLike,
                       w: Optional[ArrayLike] = None,
                       n_tasks: Optional[int] = None,
                       n_classes: int = 2,
                       per_task_metrics: bool = False,
                       use_sample_weights: bool = False,
                       **kwargs) -> Any:
        """Compute a performance metric for each task.

        Parameters
        ----------
        y_true: ArrayLike
            An ArrayLike containing true values for each task. Must be of shape
            `(N,)` or `(N, n_tasks)` or `(N, n_tasks, n_classes)` if a
            classification metric. If of shape `(N, n_tasks)` values can either be
            class-labels or probabilities of the positive class for binary
            classification problems. If a regression problem, must be of shape
            `(N,)` or `(N, n_tasks)` or `(N, n_tasks, 1)` if a regression metric.
        y_pred: ArrayLike
            An ArrayLike containing predicted values for each task. Must be
            of shape `(N, n_tasks, n_classes)` if a classification metric,
            else must be of shape `(N, n_tasks)` if a regression metric.
        w: ArrayLike, default None
            An ArrayLike containing weights for each datapoint. If
            specified,  must be of shape `(N, n_tasks)`.
        n_tasks: int, default None
            The number of tasks this class is expected to handle.
        n_classes: int, default 2
            Number of classes in data for classification tasks.
        per_task_metrics: bool, default False
            If true, return computed metric for each task on multitask dataset.
        use_sample_weights: bool, default False
            If set, use per-sample weights `w`.
        kwargs: dict
            Will be passed on to self.metric

        Returns
        -------
        np.ndarray
            A numpy array containing metric values for each task.
        """
        # Attempt some limited shape imputation to find n_tasks
        y_true_arr = np.asarray(y_true)
        y_pred_arr = np.asarray(y_pred)
        if n_tasks is None:
            if self.n_tasks is None and isinstance(y_true_arr, np.ndarray):
                if len(y_true_arr.shape) == 1:
                    n_tasks = 1
                elif len(y_true_arr.shape) >= 2:
                    n_tasks = y_true_arr.shape[1]
            else:
                n_tasks = self.n_tasks
        # check whether n_tasks is int or not
        # This is because `normalize_weight_shape` require int value.
        assert isinstance(n_tasks, int)

        y_true_arr = normalize_labels_shape(y_true_arr,
                                            mode=self.mode,
                                            n_tasks=n_tasks,
                                            n_classes=n_classes)
        y_pred_arr = normalize_prediction_shape(y_pred_arr,
                                                mode=self.mode,
                                                n_tasks=n_tasks,
                                                n_classes=n_classes)
        if self.mode == "classification":
            y_true_arr = handle_classification_mode(
                y_true_arr, self.classification_handling_mode,
                self.threshold_value)
            y_pred_arr = handle_classification_mode(
                y_pred_arr, self.classification_handling_mode,
                self.threshold_value)
        n_samples = y_true_arr.shape[0]
        w = normalize_weight_shape(None if w is None else np.asarray(w),
                                   n_samples, n_tasks)
        computed_metrics = []
        for task in range(n_tasks):
            y_task = y_true_arr[:, task]
            y_pred_arr_task = y_pred_arr[:, task]
            w_task = w[:, task]

            metric_value = self.compute_singletask_metric(
                y_task,
                y_pred_arr_task,
                w_task,
                use_sample_weights=use_sample_weights,
                **kwargs)
            computed_metrics.append(metric_value)
        logger.info("computed_metrics: %s" % str(computed_metrics))
        if n_tasks == 1:
            # FIXME: Incompatible types in assignment
            computed_metrics = computed_metrics[0]  # type: ignore

        if not per_task_metrics:
            return self.task_averager(computed_metrics)
        else:
            return self.task_averager(computed_metrics), computed_metrics

    def compute_singletask_metric(self,
                                  y_true: ArrayLike,
                                  y_pred: ArrayLike,
                                  w: Optional[ArrayLike] = None,
                                  n_samples: Optional[int] = None,
                                  use_sample_weights: bool = False,
                                  **kwargs) -> float:
        """Compute a metric value.

        Parameters
        ----------
        y_true: ArrayLike
            True values array. This array must be of shape `(N,
            n_classes)` if classification and `(N,)` if regression.
        y_pred: ArrayLike
            Predictions array. This array must be of shape `(N, n_classes)`
            if classification and `(N,)` if regression.
        w: ArrayLike, default None
            Sample weight array. This array must be of shape `(N,)`
        n_samples: int, default None (DEPRECATED)
            The number of samples in the dataset. This is `N`. This argument is
            ignored.
        use_sample_weights: bool, default False
            If set, use per-sample weights `w`.
        kwargs: dict
            Will be passed on to self.metric

        Returns
        -------
        metric_value: float
            The computed value of the metric.
        """
        if n_samples is not None:
            logger.warning(
                "n_samples is a deprecated argument which is ignored.")
        # Attempt to convert both into the same type
        y_true_arr = np.asarray(y_true)
        y_pred_arr = np.asarray(y_pred)
        if self.mode == "regression":
            if len(y_true_arr.shape) != 1 or len(
                    y_pred_arr.shape
            ) != 1 or y_true_arr.shape != y_pred_arr.shape:
                raise ValueError(
                    "For regression metrics, y_true and y_pred must both be of shape (N,)"
                )
        elif self.mode == "classification":
            pass
            # if len(y_true.shape) != 2 or len(y_pred.shape) != 2 or y_true.shape != y_pred.shape:
            # raise ValueError("For classification metrics, y_true and y_pred must both be of shape (N, n_classes)")
        else:
            raise ValueError(
                "Only classification and regression are supported for metrics calculations."
            )
        if use_sample_weights:
            metric_value = self.metric(y_true_arr,
                                       y_pred_arr,
                                       sample_weight=w,
                                       **kwargs)
        else:
            metric_value = self.metric(y_true_arr, y_pred_arr, **kwargs)
        return metric_value