问题描述
给定 Torch 中的一维张量 (torch.Tensor)，其中包含可以比较的值(比如浮点数)，我们如何提取 top-k 的索引 张量中的值?
Given a 1-D tensor in Torch (torch.Tensor), containing values which can be compared (say floating point), how can we extract the indices of the top-k values in that tensor?
除了蛮力方法之外，我正在寻找 Torch/lua 提供的一些 API 调用，它可以有效地执行此任务.
Apart from the brute-force method, I am looking for some API call, that Torch/lua provides, which can perform this task efficiently.
推荐答案
截至拉取请求 #496 Torch 现在包含一个名为 torch.topk.示例:
As of pull request #496 Torch now includes a built-in API named torch.topk. Example:
> t = torch.Tensor{9, 1, 8, 2, 7, 3, 6, 4, 5}
-- obtain the 3 smallest elements
> res = t:topk(3)
> print(res)
1
2
3
[torch.DoubleTensor of size 3]
-- you can also get the indices in addition
> res, ind = t:topk(3)
> print(ind)
2
4
6
[torch.LongTensor of size 3]
-- alternatively you can obtain the k largest elements as follow
-- (see the API documentation for more details)
> res = t:topk(3, true)
> print(res)
9
8
7
[torch.DoubleTensor of size 3]
在撰写本文时，CPU 实现遵循 排序和缩小方法(有计划在未来改进它).也就是说，目前正在审查.
At the time of writing the CPU implementation follows a sort and narrow approach (there are plans to improve it in the future). That being said an optimized GPU implementation for cutorch is currently being reviewed.
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