manipulation.py

#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import print_function

from ..fluid.layers import core, reshape
from ..fluid.layer_helper import LayerHelper
from ..fluid.framework import Variable, OpProtoHolder, in_dygraph_mode, convert_np_dtype_to_dtype_
from ..fluid.data_feeder import convert_dtype, check_variable_and_dtype, check_type, check_dtype
from ..fluid.layers.tensor import fill_constant
from ..fluid.layers import utils
import numpy as np
# TODO: define functions to manipulate a tensor  
from ..fluid.layers import cast  #DEFINE_ALIAS
from ..fluid.layers import expand  #DEFINE_ALIAS
from ..fluid.layers import expand_as  #DEFINE_ALIAS
from ..fluid.layers import flatten  #DEFINE_ALIAS
from ..fluid.layers import reshape  #DEFINE_ALIAS
from ..fluid.layers import scatter  #DEFINE_ALIAS
from ..fluid.layers import slice  #DEFINE_ALIAS
from ..fluid.layers import strided_slice  #DEFINE_ALIAS
from ..fluid.layers import transpose  #DEFINE_ALIAS
from ..fluid.layers import unique  #DEFINE_ALIAS
from ..fluid.layers import unstack  #DEFINE_ALIAS

from ..fluid.layers import gather_nd  #DEFINE_ALIAS
from ..fluid.layers import scatter_nd_add  #DEFINE_ALIAS
from ..fluid.layers import scatter_nd  #DEFINE_ALIAS
from ..fluid.layers import shard_index  #DEFINE_ALIAS
from ..fluid.layers import unique_with_counts  #DEFINE_ALIAS
from ..fluid import layers
import paddle

__all__ = [
    'cast', 'concat', 'expand', 'expand_as', 'flatten', 'gather', 'gather_nd',
    'reshape', 'reverse', 'scatter', 'scatter_nd_add', 'scatter_nd',
    'shard_index', 'slice', 'split', 'squeeze', 'stack', 'strided_slice',
    'transpose', 'unique', 'unique_with_counts', 'unsqueeze', 'unstack', 'flip',
    'unbind', 'roll'
]


def concat(x, axis=0, name=None):
    """
	:alias_main: paddle.concat
	:alias: paddle.concat,paddle.tensor.concat,paddle.tensor.manipulation.concat

    This OP concatenates the input along the axis.

    Args:
        x(list): List of input Tensors with data type float16, float32, float64, int32, int64.
            All the Tensors in ``x`` must have same data type.
        axis(int|Variable, optional): Specify the axis to operate on the input Tensors.
            It's a scalar with type ``int`` or a ``Tensor`` with shape [1] and data type ``int32`` 
            or ``int64``. The effective range is [-R, R), where R is Rank(x). When ``axis < 0``,
            it works the same way as axis+R. Default is 0.
        name (str, optional): The default value is None. Normally there is no
            need for user to set this property. For more information, please
            refer to :ref:`api_guide_Name`.
    Raises:
        TypeError: The dtype of ``x`` must be one of float16, float32, float64, int32 and int64. 
        TypeError: The ``axis`` must be int or Variable. The dtype of ``axis`` must be int32 or int64 when it's a Tensor.
        TypeError: All the Tensors in ``x`` must have the same data type.

    Returns:
        Variable: A Tensor with the same data type as ``x``.

    Examples:
        .. code-block:: python
            
            import paddle
            import numpy as np
            
            paddle.enable_imperative()  # Now we are in imperative mode
            in1 = np.array([[1,2,3],
                            [4,5,6]])
            in2 = np.array([[11,12,13],
                            [14,15,16]])
            in3 = np.array([[21,22],
                            [23,24]])
            x1 = paddle.imperative.to_variable(in1)
            x2 = paddle.imperative.to_variable(in2)
            x3 = paddle.imperative.to_variable(in3)
            zero = paddle.full(shape=[1], dtype='int32', fill_value=0)
            # When the axis is negative, the real axis is (axis + Rank(x))
            # As follow, axis is -1, Rank(x) is 2, the real axis is 1
            out1 = paddle.concat(x=[x1,x2,x3], axis=-1)
            out2 = paddle.concat(x=[x1,x2], axis=0)
            out3 = paddle.concat(x=[x1,x2], axis=zero)
            # out1
            # [[ 1  2  3 11 12 13 21 22]
            #  [ 4  5  6 14 15 16 23 24]]
            # out2 out3
            # [[ 1  2  3]
            #  [ 4  5  6]
            #  [11 12 13]
            #  [14 15 16]]
    """
    return paddle.fluid.layers.concat(input=x, axis=axis, name=name)


def flip(x, axis, name=None):
    """
	:alias_main: paddle.flip
	:alias: paddle.flip,paddle.tensor.flip,paddle.tensor.manipulation.flip


    Reverse the order of a n-D tensor along given axis in axis.

    Args:
        x (Variable): A Tensor(or LoDTensor) with shape :math:`[N_1, N_2,..., N_k]` . The data type of the input Tensor x
            should be float32, float64, int32, int64, bool.
        axis (list): The axis(axes) to flip on. Negative indices for indexing from the end are accepted.
        name (str, optional): The default value is None.  Normally there is no need for user to set this property.
            For more information, please refer to :ref:`api_guide_Name` .

    Returns:
        Variable: Tensor or LoDTensor calculated by flip layer. The data type is same with input x.

    Examples:
        .. code-block:: python

          import paddle
          import numpy as np

          paddle.enable_imperative()

          image_shape=(3, 2, 2)
          x = np.arange(image_shape[0] * image_shape[1] * image_shape[2]).reshape(image_shape)
          x = x.astype('float32')
          img = paddle.imperative.to_variable(x)
          out = paddle.flip(img, [0,1])

          print(out) # [[[10,11][8, 9]],[[6, 7],[4, 5]] [[2, 3],[0, 1]]]
    """
    helper = LayerHelper("flip", **locals())
    check_type(x, 'X', (Variable), 'flip')
    dtype = helper.input_dtype('x')
    check_dtype(dtype, 'X',
                ['float16', 'float32', 'float64', 'int32', 'int64', 'bool'],
                'flip')
    check_type(axis, 'axis', (list, tuple), 'flip')
    if name is None:
        out = helper.create_variable_for_type_inference(dtype)
    else:
        out = helper.create_variable(name=name, dtype=dtype, persistable=False)

    helper.append_op(
        type="flip",
        inputs={"X": x},
        outputs={"Out": out},
        attrs={"axis": axis})
    return out


reverse = flip  #DEFINE_ALIAS


def roll(x, shifts, axis=None, name=None):
    """
	:alias_main: paddle.roll
	:alias: paddle.roll,paddle.tensor.roll,paddle.tensor.manipulation.roll

    Roll the `x` tensor along the given axis(axes). With specific 'shifts', Elements that 
    roll beyond the last position are re-introduced at the first according to 'shifts'. 
    If a axis is not specified, 
    the tensor will be flattened before rolling and then restored to the original shape.

    Args:
        x (Variable): The x tensor variable as input.
        shifts (int|list|tuple): The number of places by which the elements
                           of the `x` tensor are shifted.
        axis (int|list|tuple|None): axis(axes) along which to roll.

    Returns:
        Variable: A Tensor with same data type as `x`.

    Examples:
        .. code-block:: python
            import numpy as np
            import paddle
            import paddle.fluid as fluid

            data = np.array([[1.0, 2.0, 3.0],
                             [4.0, 5.0, 6.0],
                             [7.0, 8.0, 9.0]])
            paddle.enable_imperative()
            x = paddle.imperative.to_variable(data)
            out_z1 = paddle.roll(x, shifts=1)
            print(out_z1.numpy())
            #[[9. 1. 2.]
            # [3. 4. 5.]
            # [6. 7. 8.]]
            out_z2 = paddle.roll(x, shifts=1, axis=0)
            print(out_z2.numpy())
            #[[7. 8. 9.]
            # [1. 2. 3.]
            # [4. 5. 6.]]
    """
    helper = LayerHelper("roll", **locals())
    origin_shape = x.shape
    if type(shifts) == int:
        shifts = [shifts]
    if type(axis) == int:
        axis = [axis]

    len_origin_shape = len(origin_shape)
    if axis:
        for i in range(len(axis)):
            if axis[i] >= len_origin_shape or axis[i] < -len_origin_shape:
                raise ValueError(
                    "axis is out of range, it should be in range [{}, {}), but received {}".
                    format(-len_origin_shape, len_origin_shape, axis))

    if axis:
        check_type(axis, 'axis', (list, tuple), 'roll')
    check_type(shifts, 'shifts', (list, tuple), 'roll')

    if in_dygraph_mode():
        if axis is None:
            x = core.ops.reshape(x, 'shape', [-1, 1])
            axis = [0]
        out = core.ops.roll(x, 'axis', axis, 'shifts', shifts)
        return core.ops.reshape(out, 'shape', origin_shape)

    out = helper.create_variable_for_type_inference(x.dtype)

    if axis is None:
        x = reshape(x, shape=[-1, 1])
        axis = [0]

    helper.append_op(
        type='roll',
        inputs={'X': x},
        outputs={'Out': out},
        attrs={'axis': axis,
               'shifts': shifts})
    out = reshape(out, shape=origin_shape, inplace=True)
    return out


def stack(x, axis=0, out=None, name=None):
    """
	:alias_main: paddle.stack
	:alias: paddle.stack,paddle.tensor.stack,paddle.tensor.manipulation.stack


    This OP stacks all the inputs :code:`x` along axis.

    .. code-block:: text

        Case 1:

          Input:
            x[0].shape = [1, 2]
            x[0].data = [ [1.0 , 2.0 ] ]
            x[1].shape = [1, 2]
            x[1].data = [ [3.0 , 4.0 ] ]
            x[2].shape = [1, 2]
            x[2].data = [ [5.0 , 6.0 ] ]

          Attrs:
            axis = 0

          Output:
            Out.dims = [3, 1, 2]
            Out.data =[ [ [1.0, 2.0] ],
                        [ [3.0, 4.0] ],
                        [ [5.0, 6.0] ] ]


        Case 2:


          Input:
            x[0].shape = [1, 2]
            x[0].data = [ [1.0 , 2.0 ] ]
            x[1].shape = [1, 2]
            x[1].data = [ [3.0 , 4.0 ] ]
            x[2].shape = [1, 2]
            x[2].data = [ [5.0 , 6.0 ] ]


          Attrs:
            axis = 1 or axis = -2

          Output:
            Out.shape = [1, 3, 2]
            Out.data =[ [ [1.0, 2.0]
                          [3.0, 4.0]
                          [5.0, 6.0] ] ]

    Args:
        x (Variable|list(Variable)): Input :code:`x` can be a single Tensor, a :code:`list` of Tensors.
                                     If :code:`x` is a :code:`list`, the shapes of all these Tensors
                                     must be the same. Supposing input is N dims
                                     Tensors :math:`[d_0, d_1, ..., d_{n-1}]`, the output is N+1 dims
                                     Tensor :math:`[d_0, d_1, d_{axis-1}, len(x), d_{axis}, ..., d_{n-1}]`.
                                     Support data types: float32, float64, int32, int64.
        axis (int, optional): The axis along which all inputs are stacked. ``axis`` range is :math:`[-(R+1), R+1)`.
                              R is the first tensor of inputs. If ``axis`` < 0, :math:`axis=axis+rank(x[0])+1`.
                              The default value of axis is 0.

    Returns:
        Variable: The stacked Tensor, has same data type with input Tensors. Output dim is :math:`rank(x[0])+1`.

    Example:    
        .. code-block:: python
            import numpy as np
            import paddle
            import paddle.fluid as fluid

            data1 = np.array([[1.0, 2.0]])
            data2 = np.array([[3.0, 4.0]])
            data3 = np.array([[5.0, 6.0]])
            with fluid.dygraph.guard():
                x1 = fluid.dygraph.to_variable(data1)
                x2 = fluid.dygraph.to_variable(data2)
                x3 = fluid.dygraph.to_variable(data3)
                result = paddle.stack([x1, x2, x3], axis=0)
                # result shape: [3, 1, 2]
                # result value: [[[1.0, 2.0]],
                #                [[3.0, 4.0]],
                #                [[5.0, 6.0]]]
    """

    helper = LayerHelper('stack', **locals())
    axis = 0 if axis is None else axis

    if not isinstance(x, list) and not isinstance(x, tuple):
        x = [x]
    out = helper.create_variable_for_type_inference(x[0].dtype)
    if not in_dygraph_mode() and \
            x[0].desc.type() == core.VarDesc.VarType.LOD_TENSOR_ARRAY:
        assert len(x) == 1, "If the elements of 'x' in stack are Variable(LoDTensorArray), " \
                            "number of the elements must be 1, but received %s." % len(x)
        out_index = helper.create_variable_for_type_inference(dtype="int32")
        helper.append_op(
            type='tensor_array_to_tensor',
            inputs={'X': x[0]},
            outputs={'Out': [out],
                     'OutIndex': [out_index]},
            attrs={'axis': axis,
                   'use_stack': True})
    else:
        helper.append_op(
            type='stack',
            inputs={'X': x},
            outputs={'Y': out},
            attrs={'axis': axis})

    return out


def split(input, num_or_sections, dim=-1, name=None):
    """
	:alias_main: paddle.split
	:alias: paddle.split,paddle.tensor.split,paddle.tensor.manipulation.split

    Split the input tensor into multiple sub-Tensors.
    Args:
        input (Variable): The input variable which is an N-D Tensor or LoDTensor, data type being float32, float64, int32 or int64.
        num_or_sections (int|list|tuple): If :attr:`num_or_sections` is an integer,
            then the integer indicates the number of equal sized sub-Tensors
            that the Tensor will be divided into. If :attr:`num_or_sections`
            is a list or tuple, the length of it indicates the number of
            sub-Tensors and the elements in it indicate the sizes of sub-Tensors'
            :attr:`dim` dimension orderly. The length of the list mustn't be larger than the Tensor's size of :attr:`dim` .
        dim (int32|Varible, optional): A scalar with type ``int32`` or a ``Tensor`` with shape [1] and type ``int32``. The dimension along which to split. If :math:`dim < 0`, the
            dimension to split along is :math:`rank(input) + dim`. Default is -1.
        name(str, optional): The default value is None.  Normally there is no need for user to set this property.  For more information, please refer to :ref:`api_guide_Name` .
    Returns:
        list(Variable): The list of segmented Tensor variables.
    Raises:
        TypeError: num_or_sections is not int, list or tuple.
        TypeError: dim is not int or Variable.
    Example:
        .. code-block:: python
            import numpy as np
            import paddle
            import paddle.fluid as fluid
            
            with fluid.dygraph.guard():
                input_1 = np.random.random([4, 6, 6]).astype("int32")
                # input is a variable which shape is [4, 6, 6]
                input = fluid.dygraph.to_variable(input_1)

                x0, x1, x2 = paddle.split(input, num_or_sections=3, dim=1)
                # x0.shape [4, 2, 6]
                # x1.shape [4, 2, 6]
                # x2.shape [4, 2, 6]
    """
    if in_dygraph_mode():
        num = None
        attrs = ()

        if isinstance(dim, Variable):
            dim = dim.numpy()
            assert dim.shape == (1,
                                 ), "dim of type Variable should have shape [1]"
            dim = dim[0]
        dim = (len(input.shape) + dim) if dim < 0 else dim
        attrs += ('axis', dim)

        if isinstance(num_or_sections, int):
            num = num_or_sections
            attrs += ('num', num_or_sections)
        elif isinstance(num_or_sections, (list, tuple)):
            num = len(num_or_sections)
            if utils._contain_var(num_or_sections):
                raise TypeError(
                    "The type of 'num_or_sections' in split must be int or list[int] or tuple[int] in Dygraph mode, but "
                    "received %s, which contains Variable." %
                    (type(num_or_sections)))
            else:
                attrs += ('sections', list(num_or_sections))
        else:
            raise TypeError(
                "The type of 'num_or_sections' in split must be int or list in Dygraph mode, but "
                "received %s." % (type(num_or_sections)))
        return core.ops.split(input, num, *attrs)

    if not isinstance(num_or_sections, (int, list, tuple)):
        raise TypeError(
            "The type of 'num_or_sections' in split must be int, list or "
            "tuple, but received %s." % (type(num_or_sections)))
    if not isinstance(dim, (int, Variable)):
        raise TypeError(
            "The type of 'dim' in split must be int or Variable, but "
            "received %s." % (type(dim)))

    helper = LayerHelper('split', **locals())
    input_shape = input.shape
    inputs = {'X': input}
    attrs = {'num': num_or_sections if isinstance(num_or_sections, int) else 0}

    def _get_SectionsTensorList(one_list):
        tensor_list = []
        unk_dim_idx = -1
        for idx, dim_size in enumerate(one_list):
            if isinstance(dim_size, Variable):
                dim_size.stop_gradient = True
                tensor_list.append(dim_size)
            else:
                assert (isinstance(dim_size, int))
                if dim_size == -1:
                    assert unk_dim_idx == -1, (
                        "Only one value of 'num_or_section' in split can "
                        "be -1. But received num_or_section[%d] is also -1." %
                        idx)
                    unk_dim_idx = idx
                temp_out = helper.create_variable_for_type_inference('int32')
                fill_constant(
                    [1], 'int32', dim_size, force_cpu=True, out=temp_out)
                tensor_list.append(temp_out)
        return tensor_list

    if isinstance(dim, Variable):
        dim.stop_gradient = True
        inputs['AxisTensor'] = dim
    else:
        dim = (len(input_shape) + dim) if dim < 0 else dim
        attrs['axis'] = dim

    if isinstance(num_or_sections, int):
        assert num_or_sections > 1, 'num_or_sections must be more than 1.'
        if isinstance(dim, int) and input_shape[dim] > 0:
            assert input_shape[dim] % num_or_sections ==0, \
                "The input's size along the split dimension " \
                "must be evenly divisible by Attr(num_or_sections). " \
                "But %d is not evenly divisible by %d. " % (num_or_sections,input_shape[dim])
        num = num_or_sections
    else:
        if isinstance(dim, int) and input_shape[dim] > 0:
            assert len(num_or_sections) <= input_shape[
                dim], 'len(num_or_sections) must not be more than input.shape[dim].'
        num = len(num_or_sections)
        attrs['sections'] = list(
            map(lambda ele: -1 if isinstance(ele, Variable) else ele,
                num_or_sections))
        if utils._contain_var(num_or_sections):
            inputs['SectionsTensorList'] = _get_SectionsTensorList(
                num_or_sections)

    outs = [
        helper.create_variable_for_type_inference(dtype=helper.input_dtype())
        for i in range(num)
    ]
    helper.append_op(
        type='split', inputs=inputs, outputs={'Out': outs}, attrs=attrs)
    return outs


def squeeze(x, axis=None, name=None):
    """
	:alias_main: paddle.squeeze
	:alias: paddle.squeeze, paddle.tensor.squeeze, paddle.tensor.manipulation.squeeze

    This OP will squeeze the dimension(s) of size 1 of input tensor x's shape. 

    If axis is provided, it will remove the dimension(s) by given axis that of size 1. 
    If the dimension of given axis is not of size 1, the dimension remain unchanged. 
    If axis is not provided, all dims equal of size 1 will be removed.

    .. code-block:: text

        Case1:

          Input:
            x.shape = [1, 3, 1, 5]  # If axis is not provided, all dims equal of size 1 will be removed.
            axis = None
          Output:
            out.shape = [3, 5]

        Case2:

          Input:
            x.shape = [1, 3, 1, 5]  # If axis is provided, it will remove the dimension(s) by given axis that of size 1.
            axis = 0
          Output:
            out.shape = [3, 1, 5]
        
        Case4:

          Input:
            x.shape = [1, 3, 1, 5]  # If the dimension of one given axis (3) is not of size 1, the dimension remain unchanged. 
            axis = [0, 2, 3]
          Output:
            out.shape = [3, 5]

        Case4:

          Input:
            x.shape = [1, 3, 1, 5]  # If axis is negative, axis = axis + ndim (number of dimensions in x). 
            axis = [-2]
          Output:
            out.shape = [1, 3, 5]

    Args:
        input (Tensor): The input Tensor. Support data type: float32, float64, int8, int32, int64.
        axis (int|list|tuple, optional): An integer or list of integers, indicating the dimensions to be squeezed. Default is None.
                          The range of axis is :math:`[-ndim(input), ndim(input))`.
                          If axis is negative, :math:`axis = axis + ndim(input)`.
                          If axis is None, all the dimensions of input of size 1 will be removed.
        name (str, optional): Please refer to :ref:`api_guide_Name`, Default None.

    Returns:
        Tensor: Output squeezed Tensor. Data type is same as input Tensor.

    Examples:
        .. code-block:: python
            import paddle

            paddle.enable_imperative()
            
            x = paddle.rand([5, 1, 10])
            output = paddle.squeeze(x, axis=1)
            # output.shape [5, 10]

    """
    if axis is None:
        axis = []
    elif isinstance(axis, int):
        axis = [axis]
    elif isinstance(axis, tuple):
        axis = list(axis)

    return layers.squeeze(x, axis, name)


def unsqueeze(input, axes, out=None, name=None):
    """
	:alias_main: paddle.unsqueeze
	:alias: paddle.unsqueeze,paddle.tensor.unsqueeze,paddle.tensor.manipulation.unsqueeze

    Insert single-dimensional entries to the shape of a Tensor. Takes one
    required argument axes, a list of dimensions that will be inserted.
    Dimension indices in axes are as seen in the output tensor.

    For example:

    .. code-block:: text

      Given a tensor such that tensor with shape [3, 4, 5],
      then Unsqueezed tensor with axes=[0, 4] has shape [1, 3, 4, 5, 1].

    Args:
        input (Variable): The input Tensor to be unsqueezed. It is a N-D Tensor of data types float32, float64, int32.
        axes (int|list|tuple|Variable): Indicates the dimensions to be inserted. The data type is ``int32`` . If ``axes`` is a list or tuple, the elements of it should be integers or Tensors with shape [1]. If ``axes`` is an Variable, it should be an 1-D Tensor .
        name (str|None): Name for this layer.

    Returns:
        Variable: Output unsqueezed Tensor, with data type being float32, float64, int32, int64.

    Examples:
        .. code-block:: python
            import numpy as np
            import paddle
            import paddle.fluid as fluid

            with fluid.dygraph.guard():
                input_1 = np.random.random([5, 10]).astype("int32")
                # input is a variable which shape is [5, 10]
                input = fluid.dygraph.to_variable(input_1)

                output = paddle.unsqueeze(input, axes=[1])
                # output.shape [5, 1, 10]
    """
    if not isinstance(axes, (int, list, tuple, Variable)):
        raise TypeError(
            "The type of 'axes' in unsqueeze must be int, list, tuple or Variable, but "
            "received %s." % (type(axes)))
    helper = LayerHelper("unsqueeze2", **locals())
    inputs = {"X": input}
    attrs = {}

    def _to_Variable_list(one_list):
        Variable_list = []
        for ele in one_list:
            if isinstance(ele, Variable):
                ele.stop_gradient = True
                Variable_list.append(ele)
            else:
                assert (isinstance(ele, int))
                temp_out = helper.create_variable_for_type_inference('int32')
                fill_constant([1], 'int32', ele, force_cpu=True, out=temp_out)
                Variable_list.append(temp_out)
        return Variable_list

    if isinstance(axes, int):
        axes = [axes]
    if isinstance(axes, Variable):
        axes.stop_gradient = True
        inputs["AxesTensor"] = axes
    elif isinstance(axes, (list, tuple)):
        contain_var = not all(not isinstance(ele, Variable) for ele in axes)
        if contain_var:
            inputs["AxesTensorList"] = _to_Variable_list(axes)
        else:
            attrs["axes"] = axes

    out = helper.create_variable_for_type_inference(dtype=input.dtype)
    x_shape = helper.create_variable_for_type_inference(dtype=input.dtype)
    helper.append_op(
        type="unsqueeze2",
        inputs=inputs,
        attrs=attrs,
        outputs={"Out": out,
                 "XShape": x_shape})

    return out


def gather(input, index, overwrite=True):
    """
	:alias_main: paddle.gather
	:alias: paddle.gather,paddle.tensor.gather,paddle.tensor.manipulation.gather

    **Gather Layer**

    Output is obtained by gathering entries of the outer-most dimension
    of X indexed by `index` and concatenate them together.

    .. math::

        Out = X[Index]


    .. code-block:: text


                Given:

                X = [[1, 2],
                     [3, 4],
                     [5, 6]]

                Index = [1, 2]

                Then:

                Out = [[3, 4],
                       [5, 6]]
    Args:
        input (Variable): The source input tensor with rank>=1. Supported data type is
            int32, int64, float32, float64 and uint8 (only for CPU),
            float16 (only for GPU).
        index (Variable): The index input tensor with rank=1. Data type is int32 or int64.
        overwrite (bool, optional): The mode that updating the grad when has same index.
            If True, use the overwrite mode to update the grad of the same index,
            if False, use the accumulate mode to update the grad of the same index.
            Default value is True.



    Returns:
        output (Variable): The output is a tensor with the same rank as input.

    Examples:

        .. code-block:: python

            import numpy as np
            import paddle
            import paddle.fluid as fluid


            with fluid.dygraph.guard():
                input_1 = np.array([[1,2],[3,4],[5,6]])
                index_1 = np.array([0,1])
                input = fluid.dygraph.to_variable(input_1)
                index = fluid.dygraph.to_variable(index_1)
                output = paddle.gather(input, index)
                # expected output: [[1,2],[3,4]]
    """
    helper = LayerHelper('gather', **locals())
    dtype = helper.input_dtype()
    out = helper.create_variable_for_type_inference(dtype)
    helper.append_op(
        type="gather",
        inputs={"X": input,
                "Index": index},
        outputs={"Out": out},
        attrs={'overwrite': overwrite})
    return out


def unbind(input, axis=0):
    """
	:alias_main: paddle.tensor.unbind
	:alias: paddle.tensor.unbind,paddle.tensor.manipulation.unbind

    Removes a tensor dimension, then split the input tensor into multiple sub-Tensors.
    Args:
        input (Variable): The input variable which is an N-D Tensor, data type being float32, float64, int32 or int64.
       
        axis (int32|int64, optional): A scalar with type ``int32|int64`` shape [1]. The dimension along which to unbind. If :math:`axis < 0`, the
            dimension to unbind along is :math:`rank(input) + axis`. Default is 0.
    Returns:
        list(Variable): The list of segmented Tensor variables.

    Example:
        .. code-block:: python
            import paddle
            # input is a variable which shape is [3, 4, 5]
            input = paddle.fluid.data(
                 name="input", shape=[3, 4, 5], dtype="float32")
            [x0, x1, x2] = paddle.tensor.unbind(input, axis=0)
            # x0.shape [4, 5]
            # x1.shape [4, 5]
            # x2.shape [4, 5]
            [x0, x1, x2, x3] = paddle.tensor.unbind(input, axis=1)
            # x0.shape [3, 5]
            # x1.shape [3, 5]
            # x2.shape [3, 5]
            # x3.shape [3, 5]

    """
    helper = LayerHelper("unbind", **locals())
    check_type(input, 'input', (Variable), 'unbind')
    dtype = helper.input_dtype()
    check_dtype(dtype, 'unbind', ['float32', 'float64', 'int32', 'int64'],
                'unbind')
    if not isinstance(axis, (int)):
        raise TypeError("The type of 'axis'  must be int, but received %s." %
                        (type(axis)))
    if isinstance(axis, np.generic):
        axis = np.asscalar(axis)
    input_shape = input.shape
    axis_ = axis if axis >= 0 else len(input_shape) + axis
    num = input_shape[axis_]
    outs = [
        helper.create_variable_for_type_inference(dtype=helper.input_dtype())
        for i in range(num)
    ]

    helper.append_op(
        type="unbind",
        inputs={"X": input},
        outputs={"Out": outs},
        attrs={"axis": axis})
    return outs