# ft_lsh

##### Feature Tranformation -- LSH (Estimator)

Locality Sensitive Hashing functions for Euclidean distance (Bucketed Random Projection) and Jaccard distance (MinHash).

##### Usage

```
ft_bucketed_random_projection_lsh(x, input_col, output_col, bucket_length,
num_hash_tables = 1L, seed = NULL, dataset = NULL,
uid = random_string("bucketed_random_projection_lsh_"), ...)
```ft_minhash_lsh(x, input_col, output_col, num_hash_tables = 1L, seed = NULL,
dataset = NULL, uid = random_string("minhash_lsh_"), ...)

##### Arguments

- x
A

`spark_connection`

,`ml_pipeline`

, or a`tbl_spark`

.- input_col
The name of the input column.

- output_col
The name of the output column.

- bucket_length
The length of each hash bucket, a larger bucket lowers the false negative rate. The number of buckets will be (max L2 norm of input vectors) / bucketLength.

- num_hash_tables
Number of hash tables used in LSH OR-amplification. LSH OR-amplification can be used to reduce the false negative rate. Higher values for this param lead to a reduced false negative rate, at the expense of added computational complexity.

- seed
A random seed. Set this value if you need your results to be reproducible across repeated calls.

- dataset
(Optional) A

`tbl_spark`

. If provided, eagerly fit the (estimator) feature "transformer" against`dataset`

. See details.- uid
A character string used to uniquely identify the feature transformer.

- ...
Optional arguments; currently unused.

##### Details

When `dataset`

is provided for an estimator transformer, the function
internally calls `ml_fit()`

against `dataset`

. Hence, the methods for
`spark_connection`

and `ml_pipeline`

will then return a `ml_transformer`

and a `ml_pipeline`

with a `ml_transformer`

appended, respectively. When
`x`

is a `tbl_spark`

, the estimator will be fit against `dataset`

before
transforming `x`

.

When `dataset`

is not specified, the constructor returns a `ml_estimator`

, and,
in the case where `x`

is a `tbl_spark`

, the estimator fits against `x`

then
to obtain a transformer, which is then immediately used to transform `x`

.

##### Value

The object returned depends on the class of `x`

.

`spark_connection`

: When`x`

is a`spark_connection`

, the function returns a`ml_transformer`

, a`ml_estimator`

, or one of their subclasses. The object contains a pointer to a Spark`Transformer`

or`Estimator`

object and can be used to compose`Pipeline`

objects.`ml_pipeline`

: When`x`

is a`ml_pipeline`

, the function returns a`ml_pipeline`

with the transformer or estimator appended to the pipeline.`tbl_spark`

: When`x`

is a`tbl_spark`

, a transformer is constructed then immediately applied to the input`tbl_spark`

, returning a`tbl_spark`

##### See Also

See http://spark.apache.org/docs/latest/ml-features.html for more information on the set of transformations available for DataFrame columns in Spark.

ft_lsh_utils

Other feature transformers: `ft_binarizer`

,
`ft_bucketizer`

,
`ft_chisq_selector`

,
`ft_count_vectorizer`

, `ft_dct`

,
`ft_elementwise_product`

,
`ft_feature_hasher`

,
`ft_hashing_tf`

, `ft_idf`

,
`ft_imputer`

,
`ft_index_to_string`

,
`ft_interaction`

,
`ft_max_abs_scaler`

,
`ft_min_max_scaler`

, `ft_ngram`

,
`ft_normalizer`

,
`ft_one_hot_encoder`

, `ft_pca`

,
`ft_polynomial_expansion`

,
`ft_quantile_discretizer`

,
`ft_r_formula`

,
`ft_regex_tokenizer`

,
`ft_sql_transformer`

,
`ft_standard_scaler`

,
`ft_stop_words_remover`

,
`ft_string_indexer`

,
`ft_tokenizer`

,
`ft_vector_assembler`

,
`ft_vector_indexer`

,
`ft_vector_slicer`

, `ft_word2vec`

*Documentation reproduced from package sparklyr, version 0.8.2, License: Apache License 2.0 | file LICENSE*