Versioned name: OneHot-1

Category: Sequence processing

Short description: OneHot sets the elements in the output tensor with specified indices to on_value and fills all other locations with off_value.

Detailed description

Taking a tensor with rank N as the first input indices, OneHot produces tensor with rank N+1 extending original tensor with a new dimension at axis position in shape. Output tensor is populated with two scalar values: on_value that comes from the 3rd input and off_value that comes from the 4nd input. Population is made in the following way:

output[:, ... ,:, i, :, ... ,:] = on_value if (indices[:, ..., :, :, ..., :] == i) else off_value

where i is at axis position in output shape and has values from range [0, ..., depth-1].

When index element from indices is greater or equal to depth, it is a well-formed operation. In this case the corresponding row output[..., i, ...] is populated with off_value only for all i values.

Types of input scalars on_value and off_value should match and can be any of the supported types. The type of output tensor is derived from on_value and off_value, they all have the same type.


  • axis
    • Description: axis is a new axis position in the output shape to fill with one-hot values.
    • Range of values: an integer. Negative value means counting dimension from the end.
    • Type: int
    • Default value: None
    • Required: yes


  • 1: indices: input tensor of rank N with indices of any supported integer data type. Can be 0D. Required.
  • 2: depth: scalar (0D tensor) of any supported integer type that specifies number of classes and the size of one-hot dimension.
  • 3: on_value: scalar (0D tensor) of any type that is the value that the locations in output tensor represented by indices in input take.
  • 4: off_value: scalar (0D tensor) of any type that is the value that the locations not represented by indices in input take.


  • 1 Output tensor of rank N+1, where N is a rank of input tensor indices. A new axis of the size depth is inserted at the dimension axis.


<layer ... type="OneHot" ...>
<data axis="-1"/>
<port id="0"> <!-- indices value: [0, 1, 2] -->
<port id="1"> <!-- depth value: 2 -->
<port id="2"> <!-- on_value 5 -->
<port id="3"> <!-- off_value 10 -->
<port id="0"> <!-- output value # [[5, 10], [10, 5], [10, 10]] -->