# Spark ML -- Gaussian Mixture clustering.

This class performs expectation maximization for multivariate Gaussian Mixture Models (GMMs). A GMM represents a composite distribution of independent Gaussian distributions with associated "mixing" weights specifying each's contribution to the composite. Given a set of sample points, this class will maximize the log-likelihood for a mixture of k Gaussians, iterating until the log-likelihood changes by less than `tol`

, or until it has reached the max number of iterations. While this process is generally guaranteed to converge, it is not guaranteed to find a global optimum.

```
ml_gaussian_mixture(x, formula = NULL, k = 2, max_iter = 100,
tol = 0.01, seed = NULL, features_col = "features",
prediction_col = "prediction", probability_col = "probability",
uid = random_string("gaussian_mixture_"), ...)
```

## Arguments

x | A |

formula | Used when |

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. |

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 |

prediction_col | Prediction column name. |

probability_col | Column name for predicted class conditional probabilities. Note: Not all models output well-calibrated probability estimates! These probabilities should be treated as confidences, not precise probabilities. |

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

... | Optional arguments, see Details. |

## 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()`

.

## See also

See http://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_kmeans`

, `ml_lda`

## Examples

```
if (FALSE) {
sc <- spark_connect(master = "local")
iris_tbl <- sdf_copy_to(sc, iris, name = "iris_tbl", overwrite = TRUE)
gmm_model <- ml_gaussian_mixture(iris_tbl, Species ~ .)
pred <- sdf_predict(iris_tbl, gmm_model)
ml_clustering_evaluator(pred)
}
```