# Updating and removing entries in sparse tensor

**URL:** <https://discuss.pytorch.org/t/updating-and-removing-entries-in-sparse-tensor/34643>\
**Category:** Uncategorized\
**Created:** [January 14, 2019, 4:44pm UTC](https://discuss.pytorch.org/t/updating-and-removing-entries-in-sparse-tensor/34643 "2019-01-14T16:44:25Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![tom0](https://discuss.pytorch.org/letter_avatar_proxy/v4/letter/t/53a042/32.png) [@tom0](https://discuss.pytorch.org/u/tom0)\
**Post date:** [January 14, 2019, 4:44pm UTC](https://discuss.pytorch.org/t/updating-and-removing-entries-in-sparse-tensor/34643/1 "2019-01-14T16:44:25Z")

</div>

I am using a sparse tensor as a kind of spike queue for my model. I am adding additional spikes to the queue by creating new sparse tensors with indices of where the new spikes should go and a list of ones as the values.

However, I am having trouble removing spikes from the queue. When I try setting the value corresponding to the index to be removed to zero and then coalesce I would expect the index to disappear but it doesn’t and the 0 values are kept in the list of values. Surprisingly the `nnz` attribute also is not changed. This means that my sparse queue is growing to be very dense with the indices of all the zeros. Also it means if I want to know if a spike exists at a location I can’t just check the presence of the index in the tensor’s indices but I also need to check the value if the index exists.

I’ve tried replacing the `_indices` and `_values` (and +`._data`) with new ones based on nonzero values but I can’t get this to work. Best I can do is just replace the entire queue with a new one, but this just defeats the point.

If I call `zero_` all of the indices and values are removed as expected.

```auto
a = (torch.rand(3,4) > 0.5).to_sparse()
'''
tensor(indices=tensor([[0, 0, 2, 2, 2],
                       [0, 3, 0, 1, 2]]),
       values=tensor([1, 1, 1, 1, 1]),
       size=(3, 4), nnz=5, dtype=torch.uint8, layout=torch.sparse_coo)
'''

a.values()[0] = 0
'''
tensor(indices=tensor([[0, 0, 2, 2, 2],
                       [0, 3, 0, 1, 2]]),
       values=tensor([0, 1, 1, 1, 1]),
       size=(3, 4), nnz=5, dtype=torch.uint8, layout=torch.sparse_coo)
'''

b = torch.zeros(3,4)
b[1,1] = 1
b = b.to(torch.uint8).to_sparse()
a += b
'''
tensor(indices=tensor([[0, 0, 1, 2, 2, 2],
                       [0, 3, 1, 0, 1, 2]]),
       values=tensor([0, 1, 1, 1, 1, 1]),
       size=(3, 4), nnz=6, dtype=torch.uint8, layout=torch.sparse_coo)
'''

a.zero_()
'''
tensor(indices=tensor([], size=(2, 0)),
       values=tensor([], size=(0,)),
       size=(3, 4), nnz=0, dtype=torch.uint8, layout=torch.sparse_coo)
'''

```

Any advice?