When I try to generate a list of permuted integer indices with randperm using the C++ PyTorch API, the resulting tensor has the element type of CPUFloatType{10} instead of an integer type:
int N_SAMPLES = 10;
torch::Tensor shuffled_indices = torch::randperm(N_SAMPLES);
cout << shuffled_indices << endl;
returns
9
3
8
6
2
5
4
7
1
0
[ CPUFloatType{10} ]
Which cannot be used used for indexing of tensors because the element type is float and not an integer type. When tryig to use my_tensor.index(shuffled_indices) I get
terminate called after throwing an instance of 'c10::IndexError'
what(): tensors used as indices must be long, byte or bool tensors
Environment:
Why does this happen?
That's because the default type of any tensor that you create with torch is always float. If you want otherwise, you have to specify it with the TensorOptions parameter struct :
int N_SAMPLES = 10;
torch::Tensor shuffled_indices = torch::randperm(N_SAMPLES, torch::TensorOptions().dtype(at::kLong));
cout << shuffled_indices.dtype() << endl;
>>> long