feat(metrics): Add MAPEMetric for regression evaluation.

docs/source/metrics.rst

@@ -143,6 +143,11 @@ Metrics
 .. autoclass:: PSNRMetric
     :members:
 
+`Mean absolute percentage error`
+---------------------------------
+.. autoclass:: MAPEMetric
+    :members:
+
 `Structural similarity index measure`
 -------------------------------------
 .. autoclass:: monai.metrics.regression.SSIMMetric

monai/metrics/__init__.py

@@ -28,6 +28,7 @@
 from .panoptic_quality import PanopticQualityMetric, compute_panoptic_quality
 from .regression import (
     MAEMetric,
+    MAPEMetric,
     MSEMetric,
     MultiScaleSSIMMetric,
     PSNRMetric,

monai/metrics/regression.py

@@ -143,6 +143,39 @@ def _compute_metric(self, y_pred: torch.Tensor, y: torch.Tensor) -> torch.Tensor
         return compute_mean_error_metrics(y_pred, y, func=self.abs_func)
 
 
+class MAPEMetric(RegressionMetric):
+    r"""Compute Mean Absolute Percentage Error between two tensors using function:
+
+    .. math::
+        \operatorname {MAPE}\left(Y, \hat{Y}\right) =\frac {100}{n}\sum _{i=1}^{n}\left|\frac{y_i-\hat{y_i}}{y_i}\right|.
+
+    More info: https://en.wikipedia.org/wiki/Mean_absolute_percentage_error
+
+    Input `y_pred` is compared with ground truth `y`.
+    Both `y_pred` and `y` are expected to be real-valued, where `y_pred` is output from a regression model.
+    Note: Tackling the undefined error, a tiny epsilon value is added to the denominator part.
+
+    Example of the typical execution steps of this metric class follows :py:class:`monai.metrics.metric.Cumulative`.
+
+    Args:
+        reduction: define the mode to reduce metrics, will only execute reduction on `not-nan` values,
+            available reduction modes: {``"none"``, ``"mean"``, ``"sum"``, ``"mean_batch"``, ``"sum_batch"``,
+            ``"mean_channel"``, ``"sum_channel"``}, default to ``"mean"``. if "none", will not do reduction.
+        get_not_nans: whether to return the `not_nans` count, if True, aggregate() returns (metric, not_nans).
+        epsilon: float. Defaults to 1e-7.
+
+    """
+
+    def __init__(
+        self, reduction: MetricReduction | str = MetricReduction.MEAN, get_not_nans: bool = False, epsilon: float = 1e-7
+    ) -> None:
+        super().__init__(reduction=reduction, get_not_nans=get_not_nans)
+        self.epsilon = epsilon
+
+    def _compute_metric(self, y_pred: torch.Tensor, y: torch.Tensor) -> torch.Tensor:
+        return compute_mape_metric(y_pred, y, epsilon=self.epsilon)
+
+
 class RMSEMetric(RegressionMetric):
     r"""Compute Root Mean Squared Error between two tensors using function:
 
@@ -220,6 +253,23 @@ def compute_mean_error_metrics(y_pred: torch.Tensor, y: torch.Tensor, func: Call
     return torch.mean(flt(func(y - y_pred)), dim=-1, keepdim=True)
 
 
+def compute_mape_metric(y_pred: torch.Tensor, y: torch.Tensor, epsilon: float = 1e-7) -> torch.Tensor:
+    """
+    Compute Mean Absolute Percentage Error.
+
+    Args:
+        y_pred: predicted values
+        y: ground truth values
+        epsilon: small value to avoid division by zero
+
+    Returns:
+        MAPE value as percentage
+    """
+    flt = partial(torch.flatten, start_dim=1)
+    percentage_error = torch.abs(y - y_pred) / torch.clamp(torch.abs(y), min=epsilon) * 100.0
+    return torch.mean(flt(percentage_error), dim=-1, keepdim=True)
+
+
 class KernelType(StrEnum):
     GAUSSIAN = "gaussian"
     UNIFORM = "uniform"

tests/metrics/test_compute_regression_metrics.py

@@ -17,7 +17,7 @@
 import numpy as np
 import torch
 
-from monai.metrics import MAEMetric, MSEMetric, PSNRMetric, RMSEMetric
+from monai.metrics import MAEMetric, MAPEMetric, MSEMetric, PSNRMetric, RMSEMetric
 from monai.utils import set_determinism
 
 
@@ -44,14 +44,19 @@ def psnrmetric_np(max_val, y_pred, y):
     return np.mean(20 * np.log10(max_val) - 10 * np.log10(mse))
 
 
+def mapemetric_np(y_pred, y, epsilon=1e-7):
+    percentage_error = np.abs(y - y_pred) / np.clip(np.abs(y), a_min=epsilon, a_max=None) * 100.0
+    return np.mean(flatten(percentage_error))
+
+
 class TestRegressionMetrics(unittest.TestCase):
 
     def test_shape_reduction(self):
         set_determinism(seed=123)
         device = "cuda" if torch.cuda.is_available() else "cpu"
 
         # regression metrics to check
-        metrics = [MSEMetric, MAEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
+        metrics = [MSEMetric, MAEMetric, MAPEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
 
         # define variations in batch/base_dims/spatial_dims
         batch_dims = [1, 2, 4, 16]
@@ -94,8 +99,8 @@ def test_compare_numpy(self):
         device = "cuda" if torch.cuda.is_available() else "cpu"
 
         # regression metrics to check + truth metric function in numpy
-        metrics = [MSEMetric, MAEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
-        metrics_np = [msemetric_np, maemetric_np, rmsemetric_np, partial(psnrmetric_np, max_val=1.0)]
+        metrics = [MSEMetric, MAEMetric, MAPEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
+        metrics_np = [msemetric_np, maemetric_np, mapemetric_np, rmsemetric_np, partial(psnrmetric_np, max_val=1.0)]
 
         # define variations in batch/base_dims/spatial_dims
         batch_dims = [1, 2, 4, 16]
@@ -117,14 +122,14 @@ def test_compare_numpy(self):
                         out_tensor = mt.aggregate(reduction="mean")
                         out_np = mt_fn_np(y_pred=in_tensor_a.cpu().numpy(), y=in_tensor_b.cpu().numpy())
 
-                        np.testing.assert_allclose(out_tensor.cpu().numpy(), out_np, atol=1e-4)
+                        np.testing.assert_allclose(out_tensor.cpu().numpy(), out_np, atol=1e-3, rtol=1e-4)
 
     def test_ill_shape(self):
         set_determinism(seed=123)
         device = "cuda" if torch.cuda.is_available() else "cpu"
 
         # regression metrics to check + truth metric function in numpy
-        metrics = [MSEMetric, MAEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
+        metrics = [MSEMetric, MAEMetric, MAPEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
         basedim = 10
 
         # too small shape
@@ -143,8 +148,8 @@ def test_ill_shape(self):
     def test_same_input(self):
         set_determinism(seed=123)
         device = "cuda" if torch.cuda.is_available() else "cpu"
-        metrics = [MSEMetric, MAEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
-        results = [0.0, 0.0, 0.0, float("inf")]
+        metrics = [MSEMetric, MAEMetric, MAPEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
+        results = [0.0, 0.0, 0.0, 0.0, float("inf")]
 
         # define variations in batch/base_dims/spatial_dims
         batch_dims = [1, 2, 4, 16]
@@ -168,8 +173,8 @@ def test_same_input(self):
     def test_diff_input(self):
         set_determinism(seed=123)
         device = "cuda" if torch.cuda.is_available() else "cpu"
-        metrics = [MSEMetric, MAEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
-        results = [1.0, 1.0, 1.0, 0.0]
+        metrics = [MSEMetric, MAEMetric, MAPEMetric, RMSEMetric, partial(PSNRMetric, max_val=1.0)]
+        results = [1.0, 1.0, 100.0, 1.0, 0.0]
 
         # define variations in batch/base_dims/spatial_dims
         batch_dims = [1, 2, 4, 16]