roboflow/supervision · error · ValueError

Predictions and targets must be lists of numpy arrays. Got {

Error message

Predictions and targets must be lists of numpy arrays. Got {type(predictions[0])} and {type(targets[0])} instead.

What it means

Error "Predictions and targets must be lists of numpy arrays. Got {type(predictions[0])} and {type(targets[0])} instead." thrown in roboflow/supervision.

Source

Thrown at src/supervision/metrics/detection.py:198

def _validate_input_tensors(
    predictions: list[npt.NDArray[np.float32]],
    targets: list[npt.NDArray[np.float32]],
    metric_target: MetricTarget = MetricTarget.BOXES,
) -> None:
    """
    Checks for shape consistency of input tensors.
    """
    if len(predictions) != len(targets):
        raise ValueError(
            f"Number of predictions ({len(predictions)}) and"
            f"targets ({len(targets)}) must be equal."
        )
    if len(predictions) > 0:
        if not isinstance(predictions[0], np.ndarray) or not isinstance(
            targets[0], np.ndarray
        ):
            raise ValueError(
                "Predictions and targets must be lists of numpy arrays. "
                f"Got {type(predictions[0])} and {type(targets[0])} instead."
            )

        expected_pred_cols = (
            10 if metric_target == MetricTarget.ORIENTED_BOUNDING_BOXES else 6
        )
        expected_target_cols = (
            9 if metric_target == MetricTarget.ORIENTED_BOUNDING_BOXES else 5
        )

        if predictions[0].shape[1] != expected_pred_cols:
            raise ValueError(
                f"Predictions must have shape (N, {expected_pred_cols}). "
                f"Got {predictions[0].shape} instead."
            )
        if targets[0].shape[1] != expected_target_cols:
            raise ValueError(

View on GitHub (pinned to 7f254d9784)

Solutions

1. Pass predictions and targets as lists of numpy arrays (one array per image).
2. Convert Detections to arrays with the appropriate helper, or convert your data to np.ndarray lists first.

When it happens

Trigger: Thrown at src/supervision/metrics/detection.py:198 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of roboflow/supervision@7f254d9784 (2026-08-15). Data as JSON: /api/errors/927429e2b54ec82e. Report an issue: GitHub.