In TensorFlow, how can I get nonzero values and their indices from a tensor with python?
I want to do something like this.
Let's say we have a tensor A.
A = [[1,0],[0,4]]
And I want to get nonzero values and their indices from it.
Nonzero values: [1,4]
Nonzero indices: [[0,0],[1,1]]
There are similar operations in Numpy.
np.flatnonzero(A) return indices that are non-zero in the flattened A.
x.ravel()[np.flatnonzero(x)] extract elements according to non-zero indices.
Here's a link for these operations.
How can I do somthing like above Numpy operations in Tensorflow with python?
(Whether a matrix is flattened or not doesn't really matter.)
Answer
You can achieve same result in Tensorflow using not_equal and where methods.
zero = tf.constant(0, dtype=tf.float32)
where = tf.not_equal(A, zero)
where is a tensor of the same shape as A holding True or False, in the following case
[[True, False],
[False, True]]
This would be sufficient to select zero or non-zero elements from A. If you want to obtain indices you can use wheremethod as follows:
indices = tf.where(where)
where tensor has two True values so indices tensor will have two entries. where tensor has rank of two, so entries will have two indices:
[[0, 0],
[1, 1]]