在C++中，Python的数组切片有类似之处吗？

Question

在带有PyTorch的Python中，如果您有一个数组：

torch.linspace(0, 10, 10)

您可以使用例如，只使用前三个元素

reduced_tensor = torch.linspace(0, 10, 10)[:4]。

在C++/lib手电筒中对[:]数组进行切片是否有类似的方法？如果没有，我怎样才能轻易做到这一点呢？

Answer 1

是的，你可以使用切片和索引。你可以：

auto tensor = torch::linspace(0, 10, 10).index({ Slice(None, 4) });

您可以阅读更多关于索引这里的内容。

基本上如文件中所述：

主要区别在于，在Python中，索引方法不是使用类似于Python语法的[]-operator，而是使用以下索引方法： 火炬：：张量：：索引(链接) torch::Tensor::index_put_ (链接) 还需要注意的是，索引类型(如None / Ellipsis / Slice )活动在torch：：index命名空间中，建议在索引代码之前使用名称空间torch：：索引，以便方便地使用这些索引类型。

为了方便起见，这里是从我刚才提供的链接中提取的一些Python C++转换：

下面是将Python索引代码转换为C++的一些示例：

Getter
------

+----------------------------------------------------------+--------------------------------------------------------------------------------------+
| Python                                                   | C++  (assuming  using namespace torch::indexing )                                    |
+==========================================================+======================================================================================+
|  tensor[None]                                            |  tensor.index({None})                                                                |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+
|  tensor[Ellipsis, ...]                                   |  tensor.index({Ellipsis, "..."})                                                     |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+
|  tensor[1, 2]                                            |  tensor.index({1, 2})                                                                |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+
|  tensor[True, False]                                     |  tensor.index({true, false})                                                         |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+
|  tensor[1::2]                                            |  tensor.index({Slice(1, None, 2)})                                                   |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+
|  tensor[torch.tensor([1, 2])]                            |  tensor.index({torch::tensor({1, 2})})                                               |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+
|  tensor[..., 0, True, 1::2, torch.tensor([1, 2])]        |  tensor.index({"...", 0, true, Slice(1, None, 2), torch::tensor({1, 2})})            |
+----------------------------------------------------------+--------------------------------------------------------------------------------------+


Translating between Python/C++ index types
------------------------------------------

The one-to-one translation between Python and C++ index types is as follows:

+-------------------------+------------------------------------------------------------------------+
| Python                  | C++ (assuming  using namespace torch::indexing )                       |
+=========================+========================================================================+
|  None                   |  None                                                                  |
+-------------------------+------------------------------------------------------------------------+
|  Ellipsis               |  Ellipsis                                                              |
+-------------------------+------------------------------------------------------------------------+
|  ...                    |  "..."                                                                 |
+-------------------------+------------------------------------------------------------------------+
|  123                    |  123                                                                   |
+-------------------------+------------------------------------------------------------------------+
|  True                   |  true                                                                  |
+-------------------------+------------------------------------------------------------------------+
|  False                  |  false                                                                 |
+-------------------------+------------------------------------------------------------------------+
|  :  or  ::              |  Slice()  or  Slice(None, None)  or  Slice(None, None, None)           |
+-------------------------+------------------------------------------------------------------------+
|  1:  or  1::            |  Slice(1, None)  or  Slice(1, None, None)                              |
+-------------------------+------------------------------------------------------------------------+
|  :3  or  :3:            |  Slice(None, 3)  or  Slice(None, 3, None)                              |
+-------------------------+------------------------------------------------------------------------+
|  ::2                    |  Slice(None, None, 2)                                                  |
+-------------------------+------------------------------------------------------------------------+
|  1:3                    |  Slice(1, 3)                                                           |
+-------------------------+------------------------------------------------------------------------+
|  1::2                   |  Slice(1, None, 2)                                                     |
+-------------------------+------------------------------------------------------------------------+
|  :3:2                   |  Slice(None, 3, 2)                                                     |
+-------------------------+------------------------------------------------------------------------+
|  1:3:2                  |  Slice(1, 3, 2)                                                        |
+-------------------------+------------------------------------------------------------------------+
|  torch.tensor([1, 2])   |  torch::tensor({1, 2})                                                 |
+-------------------------+------------------------------------------------------------------------+