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.. _op_ai_onnx_TopK-1:

TopK - version 1
================

This page documents version **1** of operator **TopK**. See :doc:`TopK` for the latest version (since version 11).

- **Domain**: ``ai.onnx``
- **Since version**: 1

Retrieve the top-K elements along a specified axis. Given an input tensor of
shape [a_0, a_1, ..., a{n-1}] and integer argument k, return two outputs:

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    -Value tensor of shape [a_0, a_1, ..., a_{axis-1}, k, a_{axis+1}, ... a_{n-1}]
      which contains the values of the top k elements along the specified axis
    -Index tensor of shape [a_0, a_1, ..., a_{axis-1}, k, a_{axis+1}, ... a_{n-1}] which
     contains the indices of the top k elements (original indices from the input
     tensor).

Given two equivalent values, this operator uses the indices along the axis  as

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    a tiebreaker. That is, the element with the lower index will appear first.


**Inputs**

- **X** (*T*): Tensor of shape [a_0, a_1, ..., a{n-1}]

**Outputs**

- **Values** (*T*): Tensor of shape [a_0, a_1, ..., a{axis-1}, k, a{axis+1}, ... a{n-1}] containing top K values from the input tensor
- **Indices** (*I*): Tensor of shape [a_0, a_1, ..., a{axis-1}, k, a{axis+1}, ... a{n-1}] containing the corresponding input tensor indices for the top K values.

**Attributes**

- **axis** (*int*): Dimension on which to do the sort.
- **k** (*int*): Number of top elements to retrieve

**Type Constraints**

- **T**: Constrain input and output types to float tensors.
  Allowed types: tensor(double), tensor(float), tensor(float16).
- **I**: Constrain index tensor to int64
  Allowed types: tensor(int64).