Fix single-image dataset failure mode (#11694)

Co-authored-by: UltralyticsAssistant <web@ultralytics.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

tests/test_cli.py

@@ -54,8 +54,8 @@ def test_export(model):
 
 def test_rtdetr(task="detect", model="yolov8n-rtdetr.yaml", data="coco8.yaml"):
     """Test the RTDETR functionality with the Ultralytics framework."""
-    # Warning: MUST use imgsz=640
-    run(f"yolo train {task} model={model} data={data} --imgsz= 160 epochs =1, cache = disk")  # add coma, spaces to args
+    # Warning: must use imgsz=640 (note also add coma, spaces, fraction=0.25 args to test single-image training)
+    run(f"yolo train {task} model={model} data={data} --imgsz= 160 epochs =1, cache = disk fraction=0.25")
     run(f"yolo predict {task} model={model} source={ASSETS / 'bus.jpg'} imgsz=160 save save_crop save_txt")
 
 

ultralytics/data/base.py

@@ -170,7 +170,7 @@ class BaseDataset(Dataset):
             if self.augment:
                 self.ims[i], self.im_hw0[i], self.im_hw[i] = im, (h0, w0), im.shape[:2]  # im, hw_original, hw_resized
                 self.buffer.append(i)
-                if len(self.buffer) >= self.max_buffer_length:
+                if 1 < len(self.buffer) >= self.max_buffer_length:  # prevent empty buffer
                     j = self.buffer.pop(0)
                     if self.cache != "ram":
                         self.ims[j], self.im_hw0[j], self.im_hw[j] = None, None, None