# ml_kmeans

Spark ML – K-Means Clustering

## Description

K-means clustering with support for k-means|| initialization proposed by Bahmani et al. Using `ml_kmeans()`

with the formula interface requires Spark 2.0+.

## Usage

```
ml_kmeans(
x,formula = NULL,
k = 2,
max_iter = 20,
tol = 1e-04,
init_steps = 2,
init_mode = "k-means||",
seed = NULL,
features_col = "features",
prediction_col = "prediction",
uid = random_string("kmeans_"),
...
)
ml_compute_cost(model, dataset)
ml_compute_silhouette_measure(
model,
dataset,distance_measure = c("squaredEuclidean", "cosine")
)
```

## Arguments

Argument | Description |
---|---|

x | A `spark_connection` , `ml_pipeline` , or a `tbl_spark` . |

formula | Used when `x` is a `tbl_spark` . R formula as a character string or a formula. This is used to transform the input dataframe before fitting, see ft_r_formula for details. |

k | The number of clusters to create |

max_iter | The maximum number of iterations to use. |

tol | Param for the convergence tolerance for iterative algorithms. |

init_steps | Number of steps for the k-means |

init_mode | Initialization algorithm. This can be either “random” to choose random points as initial cluster centers, or “k-means |

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

features_col | Features column name, as a length-one character vector. The column should be single vector column of numeric values. Usually this column is output by `ft_r_formula` . |

prediction_col | Prediction column name. |

uid | A character string used to uniquely identify the ML estimator. |

… | Optional arguments, see Details. |

model | A fitted K-means model returned by `ml_kmeans()` |

dataset | Dataset on which to calculate K-means cost |

distance_measure | Distance measure to apply when computing the Silhouette measure. |

## Value

The object returned depends on the class of `x`

.

`spark_connection`

: When`x`

is a`spark_connection`

, the function returns an instance of a`ml_estimator`

object. The object contains a pointer to a Spark`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 clustering estimator appended to the pipeline.`tbl_spark`

: When`x`

is a`tbl_spark`

, an estimator is constructed then immediately fit with the input`tbl_spark`

, returning a clustering model.`tbl_spark`

, with`formula`

or`features`

specified: When`formula`

is specified, the input`tbl_spark`

is first transformed using a`RFormula`

transformer before being fit by the estimator. The object returned in this case is a`ml_model`

which is a wrapper of a`ml_pipeline_model`

. This signature does not apply to`ml_lda()`

.

`ml_compute_cost()`

returns the K-means cost (sum of squared distances of points to their nearest center) for the model on the given data.

`ml_compute_silhouette_measure()`

returns the Silhouette measure of the clustering on the given data.

## Examples

```
<- spark_connect(master = "local")
sc <- sdf_copy_to(sc, iris, name = "iris_tbl", overwrite = TRUE)
iris_tbl ml_kmeans(iris_tbl, Species ~ .)
```

## See Also

See https://spark.apache.org/docs/latest/ml-clustering.html for more information on the set of clustering algorithms.

Other ml clustering algorithms: `ml_bisecting_kmeans()`

, `ml_gaussian_mixture()`

, `ml_lda()`