Package org.apache.lucene.document

Class FloatField

  • All Implemented Interfaces:
    IndexableField
    public final class FloatField
extends Field

    Field that indexes float values for efficient range filtering and sorting. Here's an example usage: 

     document.add(new FloatField(name, 6.0F, Field.Store.NO));
    For optimal performance, re-use the FloatField and Document instance for more than one document: 
      FloatField field = new FloatField(name, 0.0F, Field.Store.NO);
  Document document = new Document();
  document.add(field);
 
  for(all documents) {
    ...
    field.setFloatValue(value)
    writer.addDocument(document);
    ...
  }
    See also IntField, LongField, DoubleField.

    To perform range querying or filtering against a FloatField, use NumericRangeQuery or NumericRangeFilter. To sort according to a FloatField, use the normal numeric sort types, eg SortField.Type.FLOAT. FloatField values can also be loaded directly from FieldCache.

    You may add the same field name as an FloatField to the same document more than once. Range querying and filtering will be the logical OR of all values; so a range query will hit all documents that have at least one value in the range. However sort behavior is not defined. If you need to sort, you should separately index a single-valued FloatField.

    A FloatField will consume somewhat more disk space in the index than an ordinary single-valued field. However, for a typical index that includes substantial textual content per document, this increase will likely be in the noise.

    Within Lucene, each numeric value is indexed as a trie structure, where each term is logically assigned to larger and larger pre-defined brackets (which are simply lower-precision representations of the value). The step size between each successive bracket is called the precisionStep, measured in bits. Smaller precisionStep values result in larger number of brackets, which consumes more disk space in the index but may result in faster range search performance. The default value, 4, was selected for a reasonable tradeoff of disk space consumption versus performance. You can create a custom FieldType and invoke the FieldType.setNumericPrecisionStep(int) method if you'd like to change the value. Note that you must also specify a congruent value when creating NumericRangeQuery or NumericRangeFilter. For low cardinality fields larger precision steps are good. If the cardinality is < 100, it is fair to use Integer.MAX_VALUE, which produces one term per value.

    For more information on the internals of numeric trie indexing, including the precisionStep configuration, see NumericRangeQuery. The format of indexed values is described in NumericUtils.

    If you only need to sort by numeric value, and never run range querying/filtering, you can index using a precisionStep of Integer.MAX_VALUE. This will minimize disk space consumed.

    More advanced users can instead use NumericTokenStream directly, when indexing numbers. This class is a wrapper around this token stream type for easier, more intuitive usage.

    Since:
    2.9

    • Field Detail

      • TYPE_NOT_STORED

        public static final FieldType TYPE_NOT_STORED
        Type for a FloatField that is not stored: normalization factors, frequencies, and positions are omitted.

      • TYPE_STORED

        public static final FieldType TYPE_STORED
        Type for a stored FloatField: normalization factors, frequencies, and positions are omitted.