How to replace specific values in a Tensor

C++
1

Is there a convenient way to replace all occurrences of 0 in an Tensor with 1?

I’d like to normalize my data but the std deviation of some features may happen to be 0 and since we’re dividing by it I’d like to avoid division by zero errors by replacing those zeros.

2

where to replace with 1, clamp for bounding from below. Note that very small numbers might be inconvenient, too.

Best regards

Thomas

3

Thanks for your reply. Just looked up clamp function, but it’s not exactly what I need. Specifying min=0 would not remove zeros if I get it right. Picking some value bigger 0 for min would result in legitimate small values being ‘clamped’ as well…

Some way to iterate over a Tensor’s values and overwriting them if needed would be just as fine for the time being. I’m new to PyTorch/libTorch and I’m having quite some difficulties finding stuff in the documentation and getting things up and running.

Any hints would be welcome.

4

Torch.where is what you should then use.
That said, those legitimate small values can be mean to you.
In general, it is a good idea to know what you’d do in Python (PyTorch or numpy), which most often translates to Libtorch I a straightforward way.

Best regards

Thomas

5

Thanks for the hint on torch::where(), I’ll have a look at that. I have a running model in python but data preprocessing is done in pandas/numpy there which I believe is not easily available in C++.

6

Hmmm… looking at it I find

Tensor where(const Tensor & condition, const Tensor & other) const;

Python documentation is rather pythonic and seemingly not applicable to C++ if I am not mistaken. C++ documentation is not to be found…

How am I to provide a condition like ‘value is equal to 0’ to this function in a Tensor?

7

I decided to use an accessor now, iterating over the tensor elements and comparing & setting where necessary. May not be elegant but solves the problem at hand for now. Code is like:

auto a = t.accessor<float, 1>();
		
for(int i=0; i<a.size(0); i++)
	if(a[i] == 0.0)
		a[i] = 1.0;

Thanks for your help! :smile: )