R: Feature Tranformation - StringIndexer (Estimator)

ft_string_indexer {sparklyr} | R Documentation

## Feature Tranformation – StringIndexer (Estimator)

### Description

A label indexer that maps a string column of labels to an ML column of label indices. If the input column is numeric, we cast it to string and index the string values. The indices are in `[0, numLabels)`, ordered by label frequencies. So the most frequent label gets index 0. This function is the inverse of `ft_index_to_string`.

### Usage

    ft_string_indexer(x, input_col, output_col, handle_invalid = "error",
      dataset = NULL, uid = random_string("string_indexer_"), ...)

    ml_labels(model)

### 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.
`handle_invalid` | (Spark 2.1.0+) Param for how to handle invalid entries. Options are 'skip' (filter out rows with invalid values), 'error' (throw an error), or 'keep' (keep invalid values in a special additional bucket). Default: "error"
`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.
`model` | A fitted StringIndexer model returned by `ft_string_indexer()`

### 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`

`ml_labels()` returns a vector of labels, corresponding to indices to be assigned.

### 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_index_to_string`

Other feature transformers: `ft_binarizer`, `ft_bucketizer`, `ft_chisq_selector`, `ft_count_vectorizer`, `ft_dct`, `ft_elementwise_product`, `ft_hashing_tf`, `ft_idf`, `ft_imputer`, `ft_index_to_string`, `ft_interaction`, `ft_lsh`, `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_tokenizer`, `ft_vector_assembler`, `ft_vector_indexer`, `ft_vector_slicer`, `ft_word2vec`

[Package sparklyr version 0.7.0 Index]