tf.math.unsorted_segment_sum

Computes the sum along segments of a tensor.

tf.math.unsorted_segment_sum(
    data, segment_ids, num_segments, name=None
)

Read the section on segmentation for an explanation of segments.

Computes a tensor such that \(output[i] = \sum_{j...} data[j...]\) where the sum is over tuples j... such that segment_ids[j...] == i. Unlike SegmentSum, segment_ids need not be sorted and need not cover all values in the full range of valid values.

If the sum is empty for a given segment ID i, output[i] = 0. If the given segment ID i is negative, the value is dropped and will not be added to the sum of the segment.

num_segments should equal the number of distinct segment IDs.

c = [[1,2,3,4], [5,6,7,8], [4,3,2,1]]
tf.math.unsorted_segment_sum(c, [0, 1, 0], num_segments=2).numpy()
array([[5, 5, 5, 5],
       [5, 6, 7, 8]], dtype=int32)