mindspore.ops.StridedSlice

class mindspore.ops.StridedSlice(begin_mask=0, end_mask=0, ellipsis_mask=0, new_axis_mask=0, shrink_axis_mask=0)[source]

Extracts a strided slice of a Tensor based on begin/end index and strides.

This operation extracts a fragment of size (end-begin)/strides from the given ‘input_tensor’. Starting from the beginning position, the fragment continues adding strides to the index until all dimensions are not less than the ending position.

Note

  • begin 、 end and strides must have the same shape.

  • begin 、 end and strides are all 1-D Tensor, and their shape size must not greater than the dim of input_x.

During the slicing process, the fragment (end-begin)/strides are extracted from each dimension. Example: For a 5*6*7 Tensor input_x, set begin, end and strides to (1, 3, 2), (3, 5, 6), (1, 1, 2) respectively, then elements from index 1 to 3 are extrected for dim 0, index 3 to 5 are extrected for dim 1 and index 2 to 6 with a stirded of 2 are extrected for dim 2, this process is equivalent to a pythonic slice input_x[1:3, 3:5, 2:6:2].

If the length of begin 、 end and strides is smaller than the dim of input_x, then all elements are extracted from the missing dims, it behaves like all the missing dims are filled with zeros, size of that missing dim and ones. Example: For a 5*6*7 Tensor input_x, set begin, end and strides to (1, 3), (3, 5), (1, 1) respectively, then elements from index 1 to 3 are extrected for dim 0, index 3 to 5 are extrected for dim 1 and index 3 to 5 are extrected for dim 2, this process is equivalent to a pythonic slice input_x[1:3, 3:5, 0:7].

Here’s how a mask works: For each specific mask, it will be converted to a binary representation internally, and then reverse the result to start the calculation. For a 5*6*7 Tensor with a given mask value of 3 which can be represented as 0b011. Reverse that we get 0b110, which implies the first and second dim of the original Tensor will be effected by this mask. See examples below, for simplicity all mask mentioned below are all in their reverted binary form:

  • begin_mask and end_mask

    If the ith bit of begin_mask is 1, begin[i] is ignored and the fullest possible range in that dimension is used instead. end_mask is analogous, except with the end range. For a 5*6*7*8 Tensor input_x, if begin_mask is 0b110, end_mask is 0b011, the slice input_x[0:3, 0:6, 2:7:2] is produced.

  • ellipsis_mask

    If the ith bit of ellipsis_mask is 1, as many unspecified dimensions as needed will be inserted between other dimensions. Only one non-zero bit is allowed in ellipsis_mask. For a 5*6*7*8 Tensor input_x, input_x[2:,…,:6] is equivalent to input_x[2:5,:,:,0:6] , input_x[2:,…] is equivalent to input_x[2:5,:,:,:].

  • new_axis_mask

    If the ith bit of new_axis_mask is 1, begin, end and strides are ignored and a new length 1 dimension is added at the specified position in the output Tensor. For a 5*6*7 Tensor input_x, if new_axis_mask is 0b110, a new dim is added to the second dim, which will produce a Tensor with shape \((5, 1, 6, 7)\).

  • shrink_axis_mask

    If the ith bit of shrink_axis_mask is 1, begin, end and strides are ignored and dimension i will be shrunk to 0. For a 5*6*7 Tensor input_x, if shrink_axis_mask is 0b010`, it is equivalent to slice x[:, 5, :] and results in an output shape of \((5, 7)\).

Note

new_axis_mask and shrink_axis_mask are not recommended to use at the same time, it might incur unexpected result.

Parameters

  • begin_mask (int, optional) – Starting index of the slice. Default: 0.

  • end_mask (int, optional) – Ending index of the slice. Default: 0.

  • ellipsis_mask (int, optional) – An int mask, ignore slicing operation when set to 1. Default: 0.

  • new_axis_mask (int, optional) – An int mask for adding new dims. Default: 0.

  • shrink_axis_mask (int, optional) – An int mask for shrinking dims. Default: 0.

Inputs:

  • input_x (Tensor) - The input Tensor to be extracted from.

  • begin (tuple[int]) - A tuple which represents the location where to start. Only non-negative int is allowed.

  • end (tuple[int]) - A tuple or which represents the maximum location where to end. Only non-negative int is allowed.

  • strides (tuple[int]) - A tuple which represents the strides is continuously added before reaching the maximum location. Only int is allowed, it can be negative which results in reversed slicing.

Outputs:

Tensor, return the extracts a strided slice of a Tensor based on begin/end index and strides.

Raises

  • TypeError – If begin_mask, end_mask, ellipsis_mask, new_axis_mask or shrink_axis_mask is not an int.

  • TypeError – If begin 、 end or strides is not tuple[int].

  • ValueError – If begin_mask, end_mask, ellipsis_mask, new_axis_mask or shrink_axis_mask is less than 0.

  • ValueError – If begin 、 end and strides have different shapes.

Supported Platforms:

Ascend GPU CPU

Examples

>>> input_x = Tensor([[[1, 1, 1], [2, 2, 2]], [[3, 3, 3], [4, 4, 4]],
...                   [[5, 5, 5], [6, 6, 6]]], mindspore.float32)
>>> output = ops.strided_slice(input_x, (1, 0, 2), (3, 1, 3), (1, 1, 1))
>>> # Take this " output = strided_slice(input_x, (1, 0, 2), (3, 1, 3), (1, 1, 1)) " as an example,
>>> # start = [1, 0, 2] , end = [3, 1, 3], strides = [1, 1, 1], Find a segment of (start, end),
>>> # note that end is an open interval
>>> # To facilitate understanding, this operator can be divided into three steps:
>>> # Step 1: Calculation of the first dimension:
>>> # start = 1, end = 3, strides = 1, So can take 1st, 2nd rows, and then gets the final output at this time.
>>> # output_1th =
>>> # [
>>> #     [
>>> #         [3,3,3]
>>> #         [4,4,4]
>>> #     ]
>>> #     [
>>> #         [5,5,5]
>>> #         [6,6,6]
>>> #     ]
>>> # ]
>>> # Step 2: Calculation of the second dimension
>>> # 2nd dimension, start = 0, end = 1, strides = 1. So only 0th rows
>>> # can be taken, and the output at this time.
>>> # output_2nd =
>>> # [
>>> #     [
>>> #         [3,3,3]
>>> #     ]
>>> #     [
>>> #         [5,5,5]
>>> #     ]
>>> # ]
>>> # Step 3: Calculation of the third dimension
>>> # 3nd dimension,start = 2, end = 3, strides = 1, So can take 2th cols,
>>> # and you get the final output at this time.
>>> # output_3ed =
>>> # [
>>> #     [
>>> #         [3]
>>> #     ]
>>> #     [
>>> #         [5]
>>> #     ]
>>> # ]
>>> # The final output after finishing is:
>>> print(output)
[[[3.]]
 [[5.]]]
>>> # another example like :
>>> output = strided_slice(input_x, (1, 0, 0), (2, 1, 3), (1, 1, 1))
>>> print(output)
[[[3. 3. 3.]]]