class mindspore.ops.UnsortedSegmentSum(*args, **kwargs)[source]

Computes the sum of a tensor along segments.

Calculates a tensor such that \(\text{output}[i] = \sum_{segment\_ids[j] == i} \text{data}[j, \ldots]\), where \(j\) is a tuple describing the index of element in data. segment_ids selects which elements in data to sum up. Segment_ids does not need to be sorted, and it does not need to cover all values in the entire valid value range.


If the segment_id i is absent in the segment_ids, then output[i] will be filled with 0.

If the sum of the given segment_ids \(i\) is empty, then \(\text{output}[i] = 0\). If the given segment_ids is negative, the value will be ignored. ‘num_segments’ must be equal to the number of different segment_ids.

  • input_x (Tensor) - The shape is \((x_1, x_2, ..., x_R)\).

  • segment_ids (Tensor) - Set the shape as \((x_1, x_2, ..., x_N)\), where 0 < N <= R. Type must be int.

  • num_segments (int) - Set \(z\) as num_segments.


Tensor, the shape is \((z, x_{N+1}, ..., x_R)\).

  • TypeError – If num_segments is not an int.

  • ValueError – If length of shape of segment_ids is less than 1.

Supported Platforms:

Ascend GPU CPU


>>> input_x = Tensor([1, 2, 3, 4], mindspore.float32)
>>> segment_ids = Tensor([0, 0, 1, 2], mindspore.int32)
>>> num_segments = 4
>>> output = ops.UnsortedSegmentSum()(input_x, segment_ids, num_segments)
>>> print(output)
[3. 3. 4. 0.]