R: Prepare a Spark DataFrame for Spark ML Routines

ml_prepare_dataframe {sparklyr} | R Documentation

## Prepare a Spark DataFrame for Spark ML Routines

### Description

This routine prepares a Spark DataFrame for use by Spark ML routines.

### Usage

    ml_prepare_dataframe(x, features, response = NULL, ...,
      ml.options = ml_options(), envir = new.env(parent = emptyenv()))

### Arguments

`x` | An object coercable to a Spark DataFrame (typically, a `tbl_spark`).
`features` | The name of features (terms) to use for the model fit.
`response` | The name of the response vector (as a length-one character vector), or a formula, giving a symbolic description of the model to be fitted. When `response` is a formula, it is used in preference to other parameters to set the `response`, `features`, and `intercept` parameters (if available). Currently, only simple linear combinations of existing parameters is supposed; e.g. `response ~ feature1 + feature2 + ...`. The intercept term can be omitted by using `- 1` in the model fit.
`...` | Optional arguments. The `data` argument can be used to specify the data to be used when `x` is a formula; this allows calls of the form `ml_linear_regression(y ~ x, data = tbl)`, and is especially useful in conjunction with `do`.
`ml.options` | Optional arguments, used to affect the model generated. See `ml_options` for more details.
`envir` | An R environment – when supplied, it will be filled with metadata describing the transformations that have taken place.

### Details

Spark DataFrames are prepared through the following transformations:

1. All specified columns are transformed into a numeric data type (using a simple cast for integer / logical columns, and `ft_string_indexer` for strings),

2. The `ft_vector_assembler` is used to combine the specified features into a single 'feature' vector, suitable for use with Spark ML routines.

After calling this function, the `envir` environment (when supplied) will be populated with a set of variables:

`features`: | The name of the generated `features` vector.
`response`: | The name of the generated `response` vector.
`labels`: | When the `response` column is a string vector, the `ft_string_indexer` is used to transform the vector into a [0:n) numeric vector. The ordered labels are injected here to allow for easier mapping from the [0:n) values back to the original label.

### Examples

    ## Not run:
    # example of how 'ml_prepare_dataframe' might be used to invoke
    # Spark's LinearRegression routine from the 'ml' package
    envir <- new.env(parent = emptyenv())
    tdf <- ml_prepare_dataframe(df, features, response, envir = envir)

    lr <- invoke_new(
      sc,
      "org.apache.spark.ml.regression.LinearRegression"
    )

    # use generated 'features', 'response' vector names in model fit
    model <- lr %>%
      invoke("setFeaturesCol", envir$features) %>%
      invoke("setLabelCol", envir$response)

    ## End(Not run)

[Package sparklyr version 0.5.4 Index]