Clip parts of a tensor

Question

I have a theano tensor and I would like to clip its values, but each index to a different range.

For example, if I have a vector [a,b,c] , I want to clip a to [0,1] , clip b to [2,3] and c to [3,5].

How can I do that efficiently? Thanks!

Answer 1

The theano.tensor.clip operation supports symbolic minimum and maximum values so you can pass three tensors, all of the same shape, and it will perform an element-wise clip of the first with respect to the second (minimum) and third (maximum).

This code shows two variations on this theme. v1 requires the minimum and maximum values to be passed as separate vectors while v2 allows the minimum and maximum values to be passed more like a list of pairs, represented as a two column matrix.

import theano
import theano.tensor as tt


def v1():
    x = tt.vector()
    min_x = tt.vector()
    max_x = tt.vector()
    y = tt.clip(x, min_x, max_x)
    f = theano.function([x, min_x, max_x], outputs=y)
    print f([2, 1, 4], [0, 2, 3], [1, 3, 5])


def v2():
    x = tt.vector()
    min_max = tt.matrix()
    y = tt.clip(x, min_max[:, 0], min_max[:, 1])
    f = theano.function([x, min_max], outputs=y)
    print f([2, 1, 4], [[0, 1], [2, 3], [3, 5]])


def main():
    v1()
    v2()


main()