Revert "Deprecate GroupedRandomSampler for use of memmap in place of cache"

This reverts commit bbf77c9f91.

map2map/data/__init__.py

@@ -1 +1,2 @@
 from .fields import FieldDataset
+from .sampler import GroupedRandomSampler

map2map/data/sampler.py

@@ -1,6 +1,3 @@
-"""
-Deprecated for use of memmap in place of cache
-"""
 from itertools import chain
 import torch
 from torch.utils.data import Sampler

map2map/train.py

@@ -14,7 +14,7 @@ from torch.utils.data.distributed import DistributedSampler
 from torch.utils.data import DataLoader
 from torch.utils.tensorboard import SummaryWriter
 
-from .data import FieldDataset
+from .data import FieldDataset, GroupedRandomSampler
 from .data.figures import plt_slices
 from . import models
 from .models import narrow_cast, resample, Lag2Eul