assignment into repeated indices in pytorch

torch-index-operations.ipynb

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   "source": [
    "import torch"
   ]
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     "data": {
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       "(tensor([0, 1, 2, 3, 4]), torch.Size([5]))"
      ]
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     "execution_count": 2,
     "metadata": {},
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   ],
   "source": [
    "tensor = torch.arange(5)\n",
    "tensor, tensor.shape"
   ]
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   "source": [
    "problem being solved...\n",
    "\n",
    "multiple addition into same index with fancy indexing doesn't work as expected"
   ]
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    {
     "data": {
      "text/plain": [
       "tensor([3, 1, 2, 3, 4])"
      ]
     },
     "execution_count": 3,
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   "source": [
    "tensor[[0, 0]] += torch.Tensor([5, 3]).long()\n",
    "tensor"
   ]
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   "cell_type": "code",
   "execution_count": 4,
   "id": "79a8ea6a-46c8-42de-b371-ee2e9dd8a5ac",
   "metadata": {},
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    {
     "data": {
      "text/plain": [
       "tensor([8, 1, 2, 3, 4])"
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     "execution_count": 4,
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   "source": [
    "tensor = torch.arange(5)\n",
    "tensor.index_add_(dim=0, index=torch.Tensor([0, 0]).int(), source=torch.Tensor([5, 3]).long())"
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   "source": [
    "the above doesn't support multidimensional indices\n",
    "\n",
    "c.f. https://discuss.pytorch.org/t/index-adding-over-multiple-dimensions/124709/6\n",
    "\n",
    "use `index_put` instead"
   ]
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   "execution_count": 5,
   "id": "bdb52925-90e0-4ce8-834f-a2468bfe0ebd",
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       "tensor([8, 1, 2, 3, 4])"
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     "execution_count": 5,
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   ],
   "source": [
    "tensor = torch.arange(5)\n",
    "tensor.index_put_((torch.Tensor([0, 0]).long(), ), torch.Tensor([5, 3]).long(), accumulate=True)"
   ]
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