UKBB brain age

+import logging
+import os
+
+import nibabel
+import numpy
+import pandas
+from torchvision.datasets import VisionDataset
+
+logger = logging.getLogger()
+FILEPATHKEY = "9dof_2mm_vol"
+
+
+class UKBBBrainAGE(VisionDataset):
+    @staticmethod
+    def get_path(root, path):
+        if path == "/" or root is None:
+            return path
+        return os.path.join(root, str(path))
+
+    def __init__(self, root, metadatafile, transform=None, target_transform=None, verify=False,
+                 num_sample=-1,  random_state=0):
+        super().__init__(root, transform=transform, target_transform=target_transform)
+        self.df = pandas.read_csv(metadatafile)
+
+        # do a random sample of dataset
+        if num_sample > 0:
+            # fixed seed will be useful to train multiple models with same data
+            self.df = self.df.sample(n=num_sample, random_state=random_state, replace=True)
+
+        if verify:
+            # remove all those entries for which we dont have file
+            indices = []
+            for i, row in self.df.iterrows():
+                if not os.path.exists(self.get_path(root, row[FILEPATHKEY])):
+                    indices.append(i)
+            if indices:
+                logger.info(f"Dropping {len(indices)}")
+                logger.debug(f"Dropped rows {indices}")
+            self.df = self.df.drop(index=indices)
+
+    def __getitem__(self, index):
+        row = self.df.iloc[index]
+        path = self.get_path(self.root, row[FILEPATHKEY])
+        subject_id = row["subject_id"]
+        age = row["age_at_scan"]
+        img = nibabel.load(path).get_fdata()
+        img = (img - img.mean()) / img.std()
+        scan = img[numpy.newaxis, :, :, :]
+        age = age
+
+        if self.transform:
+            scan = self.transform(scan)
+
+        if self.target_transform:
+            age = self.target_transform(age)
+
+        return numpy.float32(scan), numpy.float32(age), subject_id
+
+    def __len__(self):
+        return self.df.shape[0]
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