roboflow/supervision · error · ValueError

ConfusionMatrix can only be calculated for Detections with c

Error message

ConfusionMatrix can only be calculated for Detections with confidence

What it means

Error "ConfusionMatrix can only be calculated for Detections with confidence" thrown in roboflow/supervision.

Source

Thrown at src/supervision/metrics/detection.py:172

                raise ValueError(
                    f"Expected {ORIENTED_BOX_COORDINATES} to contain "
                    f"{len(detections) * 8} elements "
                    f"(N={len(detections)} detections x 8 coordinates), "
                    f"but got {obb_arr.size}. "
                    "Each OBB must be stored as [x1, y1, x2, y2, x3, y3, x4, y4]."
                )
            box_data = obb_arr.reshape(-1, 8)
    else:
        box_data = np.asarray(detections.xyxy, dtype=np.float32)

    arrays_to_concat = [
        box_data,
        np.expand_dims(detections.class_id.astype(np.float32), 1),
    ]

    if with_confidence:
        if detections.confidence is None:
            raise ValueError(
                "ConfusionMatrix can only be calculated for Detections with confidence"
            )
        arrays_to_concat.append(np.expand_dims(detections.confidence, 1))

    result: npt.NDArray[np.float32] = np.concatenate(arrays_to_concat, axis=1)
    return result


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(

View on GitHub (pinned to 7f254d9784)

Solutions

1. Set confidence on the prediction Detections before computing the confusion matrix.
2. If scores are unavailable, provide a placeholder confidence array.

When it happens

Trigger: Thrown at src/supervision/metrics/detection.py:172 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/2d5f213f1f9417a4. Report an issue: GitHub.