internal static IEstimator <ITransformer> CreateEstimator(IHostEnvironment env, Options options, SchemaShape inputSchema)
{
Contracts.CheckValue(env, nameof(env));
var h = env.Register(RegistrationName);
h.CheckValue(options, nameof(options));
h.CheckUserArg(Utils.Size(options.Columns) > 0, nameof(options.Columns), "Columns must be specified");
// Compose the WordBagTransform from a tokenize transform,
// followed by a NgramExtractionTransform.
// Since WordBagTransform is a many-to-one column transform, for each
// WordBagTransform.Column with multiple sources, we first apply a ConcatTransform.
// REVIEW: In order to not get n-grams that cross between vector slots, we need to
// enable tokenize transforms to insert a special token between slots.
// REVIEW: In order to make it possible to output separate bags for different columns
// using the same dictionary, we need to find a way to make ConcatTransform remember the boundaries.
var tokenizeColumns = new WordTokenizingEstimator.ColumnOptions[options.Columns.Length];
var extractorArgs =
new NgramExtractorTransform.Options()
{
MaxNumTerms = options.MaxNumTerms,
NgramLength = options.NgramLength,
SkipLength = options.SkipLength,
UseAllLengths = options.UseAllLengths,
Weighting = options.Weighting,
Columns = new NgramExtractorTransform.Column[options.Columns.Length]
};
for (int iinfo = 0; iinfo < options.Columns.Length; iinfo++)
{
var column = options.Columns[iinfo];
h.CheckUserArg(!string.IsNullOrWhiteSpace(column.Name), nameof(column.Name));
h.CheckUserArg(Utils.Size(column.Source) > 0, nameof(column.Source));
h.CheckUserArg(column.Source.All(src => !string.IsNullOrWhiteSpace(src)), nameof(column.Source));
tokenizeColumns[iinfo] = new WordTokenizingEstimator.ColumnOptions(column.Name, column.Source.Length > 1 ? column.Name : column.Source[0]);
extractorArgs.Columns[iinfo] =
new NgramExtractorTransform.Column()
{
Name = column.Name,
Source = column.Name,
MaxNumTerms = column.MaxNumTerms,
NgramLength = column.NgramLength,
SkipLength = column.SkipLength,
Weighting = column.Weighting,
UseAllLengths = column.UseAllLengths
};
}
IEstimator <ITransformer> estimator = NgramExtractionUtils.GetConcatEstimator(h, options.Columns);
estimator = estimator.Append(new WordTokenizingEstimator(env, tokenizeColumns));
estimator = estimator.Append(NgramExtractorTransform.CreateEstimator(h, extractorArgs, estimator.GetOutputSchema(inputSchema)));
return(estimator);
}
public ITransformer Create(IHostEnvironment env, IDataView input, ExtractorColumn[] cols)
{
var options = NgramExtractorTransform.CreateNgramExtractorOptions(_extractorArgs, cols);
return(NgramExtractorTransform.CreateEstimator(env, options, SchemaShape.Create(input.Schema), _termLoaderArgs).Fit(input));
}
