# GatherElements¶

Versioned name : GatherElements-6

Category : Data movement operations

Short description : GatherElements takes elements from the input data tensor at positions specified in the indices tensor.

Detailed description GatherElements takes elements from the data tensor at positions specified in the indices tensor. The data and indices tensors have the same rank r >= 1. Optional attribute axis determines along which axis elements with indices specified in indices are taken. The indices tensor has the same shape as the data tensor except for the axis dimension. Output consists of values (gathered from the data tensor) for each element in the indices tensor and has the same shape as indices.

For instance, in the 3D case (r = 3), the output is determined by the following equations:

out[i][j][k] = data[indices[i][j][k]][j][k] if axis = 0
out[i][j][k] = data[i][indices[i][j][k]][k] if axis = 1
out[i][j][k] = data[i][j][indices[i][j][k]] if axis = 2

Example 1 with concrete values:

data = [
[1, 2],
[3, 4],
]
indices = [
[0, 1],
[0, 0],
]
axis = 0
output = [
[1, 4],
[1, 2],
]

Example 2 with axis = 1 and indices having greater (than data) shape:

data = [
[1, 7],
[4, 3],
]
indices = [
[1, 1, 0],
[1, 0, 1],
]
axis = 1
output = [
[7, 7, 1],
[3, 4, 3],
]

Example 3 indices has lesser (than data) shape:

data = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
]
indices = [
[1, 0, 1],
[1, 2, 0],
]
axis = 0
output = [
[4, 2, 6],
[4, 8, 3],
]

Attributes :

• axis

• Description : Which axis to gather on. Negative value means counting dimensions from the back.

• Range of values : [-r, r-1] where r = rank(data).

• Type : int

• Required : yes

Inputs :

• 1 : Tensor of type T. This is a tensor of a rank >= 1. Required.

• 2 : Tensor of type T_IND with the same rank as the input. All index values are expected to be within bounds [0, s-1], where s is size along axis dimension of the data tensor. Required.

Outputs :

• 1 : Tensor with gathered values of type T. Tensor has the same shape as indices.

Types

• T : any supported type.

• T_IND : int32 or int64.

Example

<... type="GatherElements" ...>
<data axis="1" />
<input>
<port id="0">
<dim>3</dim>
<dim>7</dim>
<dim>5</dim>
</port>
<port id="1">
<dim>3</dim>
<dim>10</dim>
<dim>5</dim>
</port>
</input>
<output>
<port id="2">
<dim>3</dim>
<dim>10</dim>
<dim>5</dim>
</port>
</output>
</layer>