FMeasure (Apache OpenNLP Tools 1.9.5 API)
Date: 2026-06-18

opennlp.tools.util.eval

## Class FMeasure

- java.lang.Object
- - opennlp.tools.util.eval.FMeasure

-     public final class FMeasure
      extends Object

  The `FMeasure` is an utility class for evaluators which measure precision, recall and the resulting f-measure. Evaluation results are the arithmetic mean of the precision scores calculated for each reference sample and the arithmetic mean of the recall scores calculated for each reference sample.

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `FMeasure()`

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `double` | `getFMeasure()` Retrieves the f-measure score.
    `double` | `getPrecisionScore()` Retrieves the arithmetic mean of the precision scores calculated for each evaluated sample.
    `double` | `getRecallScore()` Retrieves the arithmetic mean of the recall score calculated for each evaluated sample.
    `void` | `mergeInto(FMeasure measure)` Merge results into fmeasure metric.
    `static double` | `precision(Object[] references, Object[] predictions)` Calculates the precision score for the given reference and predicted spans.
    `static double` | `recall(Object[] references, Object[] predictions)` Calculates the recall score for the given reference and predicted spans.
    `String` | `toString()` Creates a human read-able `String` representation.
    `void` | `updateScores(Object[] references, Object[] predictions)` Updates the score based on the number of true positives and the number of predictions and references.

    - ### Methods inherited from class java.lang.Object

      `equals, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### FMeasure

          public FMeasure()

  - ### Method Detail

    - #### getPrecisionScore

          public double getPrecisionScore()

      Retrieves the arithmetic mean of the precision scores calculated for each evaluated sample.
      Returns:
        the arithmetic mean of all precision scores

    - #### getRecallScore

          public double getRecallScore()

      Retrieves the arithmetic mean of the recall score calculated for each evaluated sample.
      Returns:
        the arithmetic mean of all recall scores

    - #### getFMeasure

          public double getFMeasure()

      Retrieves the f-measure score. f-measure = 2 * precision * recall / (precision + recall)
      Returns:
        the f-measure or -1 if precision + recall <= 0

    - #### updateScores

          public void updateScores(Object[] references,
                                   Object[] predictions)

      Updates the score based on the number of true positives and the number of predictions and references.
      Parameters:
        `references` - the provided references
        `predictions` - the predicted spans

    - #### mergeInto

          public void mergeInto(FMeasure measure)

      Merge results into fmeasure metric.
      Parameters:
        `measure` - the fmeasure

    - #### toString

          public String toString()

      Creates a human read-able `String` representation.
      Overrides:
        `toString` in class `Object`
      Returns:
        the results

    - #### precision

          public static double precision(Object[] references,
                                         Object[] predictions)

      Calculates the precision score for the given reference and predicted spans.
      Parameters:
        `references` - the gold standard spans
        `predictions` - the predicted spans
      Returns:
        the precision score or NaN if there are no predicted spans

    - #### recall

          public static double recall(Object[] references,
                                      Object[] predictions)

      Calculates the recall score for the given reference and predicted spans.
      Parameters:
        `references` - the gold standard spans
        `predictions` - the predicted spans
      Returns:
        the recall score or NaN if there are no reference spans

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