I need to permute elements of a tensor in TF according to a given indexing. From 2 arrays a and b(indices), I need to compute a new array that permutes the elements in a according to the indices in b. For indices that are empty, it should fill with NA (or equivalent). 

For example, 

```
a = [10, 20, 30]  
b = [-1,  0,  3]  
output = [ 10,  20,   NA,   NA,  30] 

```

I need to code the equivalent of what happens to the following numpy arrays but for TF tensors.

```
a = np.array([10,20,30])
b = np.array([-1,0,3])
mini = abs(np.min(b))
maxi = abs(np.max(b))
output = np.zeros(maxi+mini+1)
for ai,bi in zip(a,b):
    output[bi+mini]= ai

```

How do I do this with TensorFlow tensors?