# Sampling with replacement

#21

That’s a good point, you would need to find a way or relating the target label to it’s frequency in the dataset based on a known distribution of object counts.

I’ll try your method above and see how it goes!

Thanks again!

#22

Even if the distribution is unknown, we could use binning with a specified number of bins to make the labels categorical. This would allow us to treat the regression samples as classes and count their occurrences.

#23

Or one could try to work with kernel density estimation. But that is computationally way more expensive and more work.

#24

I’ve tried to implement this by first binning the data by rounding them to their closest 0.5 and then defining each of those 0.5 intervals as a class from 0-10.

I’m finding that the sampler is still preferring the rare events such as the extremely low and extremely high labelled data. Perhaps because there’s only one or two images for these ‘classes’.

I’ve observed this happening for every batch…so I’m not sure why this isn’t working at the moment as it seems to be fine in test cases such as the code snippet below:

``````numDataPoints = 1000
data_dim = 5
bs = 100

# Create dummy data with class imbalance 99 to 1
data = torch.randn(numDataPoints, data_dim)

target = np.hstack([np.random.uniform(0.055,0.5,999), np.random.uniform(0,0.04,1)])

def binner(array):
array = np.round(np.round(array*200)/20)
return array.astype(int)

target = binner(target)
target = torch.LongTensor(target)

class_sample_count = torch.tensor(
[(target == t).sum() for t in torch.unique(target, sorted=True)])
weight = 1. / class_sample_count.float()
samples_weight = torch.tensor([weight[t] for t in target])

sampler = WeightedRandomSampler(samples_weight, int(len(samples_weight)),replacement=True)

train_dataset = torch.utils.data.TensorDataset(data, target)

train_dataset, batch_size=bs, shuffle=False, num_workers=1, sampler=sampler)

for i, (x, y) in enumerate(train_loader):
print("batch index {}, 0/1/2/3/4/5...: {}/{}/{}/{}/{}/{}".format(
i, (y == 0).sum(), (y == 1).sum(), (y == 2).sum(), (y == 3).sum(), (y == 4).sum(), (y == 5).sum(), (y == 6).sum()))
``````

OUT:

``````batch index 0, 0/1/2/3/4/5...: 13/16/22/16/17/16
batch index 1, 0/1/2/3/4/5...: 10/15/24/14/15/22
batch index 2, 0/1/2/3/4/5...: 16/17/22/12/17/16
batch index 3, 0/1/2/3/4/5...: 12/14/14/21/14/25
batch index 4, 0/1/2/3/4/5...: 13/19/12/21/20/15
batch index 5, 0/1/2/3/4/5...: 13/25/18/17/13/14
batch index 6, 0/1/2/3/4/5...: 16/22/15/12/18/17
batch index 7, 0/1/2/3/4/5...: 18/18/13/22/17/12
batch index 8, 0/1/2/3/4/5...: 15/18/13/15/21/18
batch index 9, 0/1/2/3/4/5...: 16/17/16/15/23/13
``````

#25

That’s still strange, as it seems to work in the example.
Could you post the class frequencies?
Are you observing this distribution in every batch?