A preprocessing layer which hashes and bins categorical features.

```
layer_hashing(
object,
num_bins,
mask_value = NULL,
salt = NULL,
output_mode = "int",
sparse = FALSE,
...
)
```

- object
What to compose the new

`Layer`

instance with. Typically a Sequential model or a Tensor (e.g., as returned by`layer_input()`

). The return value depends on`object`

. If`object`

is:missing or

`NULL`

, the`Layer`

instance is returned.a

`Sequential`

model, the model with an additional layer is returned.a Tensor, the output tensor from

`layer_instance(object)`

is returned.

- num_bins
Number of hash bins. Note that this includes the

`mask_value`

bin, so the effective number of bins is`(num_bins - 1)`

if`mask_value`

is set.- mask_value
A value that represents masked inputs, which are mapped to index 0. Defaults to NULL, meaning no mask term will be added and the hashing will start at index 0.

- salt
A single unsigned integer or NULL. If passed, the hash function used will be SipHash64, with these values used as an additional input (known as a "salt" in cryptography). These should be non-zero. Defaults to

`NULL`

(in that case, the FarmHash64 hash function is used). It also supports list of 2 unsigned integer numbers, see reference paper for details.- output_mode
Specification for the output of the layer. Defaults to

`"int"`

. Values can be`"int"`

,`"one_hot"`

,`"multi_hot"`

, or`"count"`

configuring the layer as follows:`"int"`

: Return the integer bin indices directly.`"one_hot"`

: Encodes each individual element in the input into an array the same size as`num_bins`

, containing a 1 at the input's bin index. If the last dimension is size 1, will encode on that dimension. If the last dimension is not size 1, will append a new dimension for the encoded output.`"multi_hot"`

: Encodes each sample in the input into a single array the same size as`num_bins`

, containing a 1 for each bin index index present in the sample. Treats the last dimension as the sample dimension, if input shape is`(..., sample_length)`

, output shape will be`(..., num_tokens)`

.`"count"`

: As`"multi_hot"`

, but the int array contains a count of the number of times the bin index appeared in the sample.

- sparse
Boolean. Only applicable to

`"one_hot"`

,`"multi_hot"`

, and`"count"`

output modes. If`TRUE`

, returns a`SparseTensor`

instead of a dense`Tensor`

. Defaults to`FALSE`

.- ...
standard layer arguments.

This layer transforms single or multiple categorical inputs to hashed output.
It converts a sequence of int or string to a sequence of int. The stable hash
function uses `tensorflow::ops::Fingerprint`

to produce the same output
consistently across all platforms.

This layer uses FarmHash64 by default, which provides a consistent hashed output across different platforms and is stable across invocations, regardless of device and context, by mixing the input bits thoroughly.

If you want to obfuscate the hashed output, you can also pass a random `salt`

argument in the constructor. In that case, the layer will use the
SipHash64 hash function, with
the `salt`

value serving as additional input to the hash function.

**Example (FarmHash64)**

```
layer <- layer_hashing(num_bins=3)
inp <- matrix(c('A', 'B', 'C', 'D', 'E'))
layer(inp)
# <tf.Tensor: shape=(5, 1), dtype=int64, numpy=
# array([[1],
# [0],
# [1],
# [1],
# [2]])>
```

**Example (FarmHash64) with a mask value**

```
layer <- layer_hashing(num_bins=3, mask_value='')
inp <- matrix(c('A', 'B', 'C', 'D', 'E'))
layer(inp)
# <tf.Tensor: shape=(5, 1), dtype=int64, numpy=
# array([[1],
# [1],
# [0],
# [2],
# [2]])>
```

**Example (SipHash64)**

```
layer <- layer_hashing(num_bins=3, salt=c(133, 137))
inp <- matrix(c('A', 'B', 'C', 'D', 'E'))
layer(inp)
# <tf.Tensor: shape=(5, 1), dtype=int64, numpy=
# array([[1],
# [2],
# [1],
# [0],
# [2]])>
```

**Example (Siphash64 with a single integer, same as salt=[133, 133])**

```
layer <- layer_hashing(num_bins=3, salt=133)
inp <- matrix(c('A', 'B', 'C', 'D', 'E'))
layer(inp)
# <tf.Tensor: shape=(5, 1), dtype=int64, numpy=
# array([[0],
# [0],
# [2],
# [1],
# [0]])>
```

https://www.tensorflow.org/api_docs/python/tf/keras/layers/Hashing

https://keras.io/api/layers/preprocessing_layers/categorical/hashing/

Other categorical features preprocessing layers:
`layer_category_encoding()`

,
`layer_integer_lookup()`

,
`layer_string_lookup()`

Other preprocessing layers:
`layer_category_encoding()`

,
`layer_center_crop()`

,
`layer_discretization()`

,
`layer_integer_lookup()`

,
`layer_normalization()`

,
`layer_random_brightness()`

,
`layer_random_contrast()`

,
`layer_random_crop()`

,
`layer_random_flip()`

,
`layer_random_height()`

,
`layer_random_rotation()`

,
`layer_random_translation()`

,
`layer_random_width()`

,
`layer_random_zoom()`

,
`layer_rescaling()`

,
`layer_resizing()`

,
`layer_string_lookup()`

,
`layer_text_vectorization()`