How to change certain values in a torch tensor based on an index in another torch tensor?

Question

This is an issue I'm running while convertinf DQN to Double DQN for the cartpole problem. I'm getting close to figuring it out.

tensor([0.1205, 0.1207, 0.1197, 0.1195, 0.1204, 0.1205, 0.1208, 0.1199, 0.1206,
        0.1199, 0.1204, 0.1205, 0.1199, 0.1204, 0.1204, 0.1203, 0.1198, 0.1198,
        0.1205, 0.1204, 0.1201, 0.1205, 0.1208, 0.1202, 0.1205, 0.1203, 0.1204,
        0.1205, 0.1206, 0.1206, 0.1205, 0.1204, 0.1201, 0.1206, 0.1206, 0.1199,
        0.1198, 0.1200, 0.1206, 0.1207, 0.1208, 0.1202, 0.1201, 0.1210, 0.1208,
        0.1205, 0.1205, 0.1201, 0.1193, 0.1201, 0.1205, 0.1207, 0.1207, 0.1195,
        0.1210, 0.1204, 0.1209, 0.1207, 0.1187, 0.1202, 0.1198, 0.1202])
tensor([ True,  True,  True,  True,  True,  True,  True,  True,  True,  True,
         True,  True,  True,  True,  True,  True, False,  True,  True,  True,
         True,  True,  True,  True,  True,  True,  True, False,  True,  True,
         True,  True,  True,  True,  True,  True,  True,  True,  True,  True,
         True,  True,  True,  True,  True,  True,  True,  True,  True,  True,
         True,  True,  True,  True,  True,  True,  True,  True,  True,  True,
         True,  True,  True,  True])

As you can see here two tensors. The first has the q values I want but, some values need to be changed to zeros because of it an end state. The second tensor shows where it will be zeros.

At the index where the Boolean value is false is the equivalent spot for where the upper tensor needs to be zeros. I am not sure how to do that.

Dishin H Goyani · Answer 1 · 2020-02-28T04:49:46.213

5

You can use torch.where - torch.where(condition, x, y)

Ex.:

>>> x = tensor([0.2853, 0.5010, 0.9933, 0.5880, 0.3915, 0.0141, 0.7745,  
                0.0588, 0.4939, 0.0849])
>>> condition = tensor([False,  True,  True,  True, False, False,  True,  
                        False, False, False])

>>> # It's equivalent to `torch.where(condition, x, tensor(0.0))`
>>> x.where(condition, tensor(0.0))
tensor([0.0000, 0.5010, 0.9933, 0.5880, 0.0000, 0.0000, 0.7745,  
        0.0000, 0.0000,0.0000])

edited Feb 28 '20 at 04:49

answered Feb 28 '20 at 04:42

Dishin H Goyani

7,195
3
26
37

Direct official link: https://pytorch.org/docs/stable/generated/torch.where.html#torch.where – user3613932 May 19 '21 at 00:43

score 3 · Answer 2 · answered Feb 27 '20 at 22:01

3

If your above tensor is the value tensor and the bottom one is the decision tensor, then

value_tensor[decision_tensor==False] = 0

Moreover, you could also convert them to numpy arrays and perform the same operation and it should work.

answered Feb 27 '20 at 22:01

Anurag Reddy

1,159
11
19

How to change certain values in a torch tensor based on an index in another torch tensor?

2 Answers2