com.twitter.algebird

SpaceSaver

sealed abstract class SpaceSaver[T] extends AnyRef

Data structure used in the Space-Saving Algorithm to find the approximate most frequent and top-k elements. The algorithm is described in "Efficient Computation of Frequent and Top-k Elements in Data Streams". See here: www.cs.ucsb.edu/research/tech_reports/reports/2005-23.pdf In the paper the data structure is called StreamSummary but we chose to call it SpaceSaver instead. Note that the adaptation to hadoop and parallelization were not described in the article and have not been proven to be mathematically correct or preserve the guarantees or benefits of the algorithm.

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Known Subclasses
SSMany, SSOne
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Instance Constructors

  1. new SpaceSaver()

Abstract Value Members

  1. abstract def ++(other: SpaceSaver[T]): SpaceSaver[T]

  2. abstract def capacity: Int

    Maximum number of counters to keep (parameter "m" in the research paper).

  3. abstract def counters: Map[T, (Long, Long)]

    Map of item to counter, where each counter consists of an observed count and possible over-estimation (error)

  4. abstract def min: Long

    Current lowest value for count

Concrete Value Members

  1. final def !=(arg0: AnyRef): Boolean

    Definition Classes
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  2. final def !=(arg0: Any): Boolean

    Definition Classes
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  3. final def ##(): Int

    Definition Classes
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  4. final def ==(arg0: AnyRef): Boolean

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  5. final def ==(arg0: Any): Boolean

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  6. final def asInstanceOf[T0]: T0

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  7. def clone(): AnyRef

    Attributes
    protected[java.lang]
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    Annotations
    @throws( ... )

  8. def consistentWith(that: SpaceSaver[T]): Boolean

    Check consistency with other SpaceSaver, useful for testing.

    Check consistency with other SpaceSaver, useful for testing. Returns boolean indicating if they are consistent

  9. final def eq(arg0: AnyRef): Boolean

    Definition Classes
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  10. def equals(arg0: Any): Boolean

    Definition Classes
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  11. def finalize(): Unit

    Attributes
    protected[java.lang]
    Definition Classes
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    Annotations
    @throws( classOf[java.lang.Throwable] )

  12. def frequency(item: T): Approximate[Long]

    returns the frequency estimate for the item

  13. final def getClass(): Class[_]

    Definition Classes
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  14. def hashCode(): Int

    Definition Classes
    AnyRef → Any

  15. final def isInstanceOf[T0]: Boolean

    Definition Classes
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  16. def mostFrequent(thres: Int): Seq[(T, Approximate[Long], Boolean)]

    Get the elements that show up more than thres times.

    Get the elements that show up more than thres times. Returns sorted in descending order: (item, Approximate[Long], guaranteed)

  17. final def ne(arg0: AnyRef): Boolean

    Definition Classes
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  18. final def notify(): Unit

    Definition Classes
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  19. final def notifyAll(): Unit

    Definition Classes
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  20. final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
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  21. def toString(): String

    Definition Classes
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  22. def topK(k: Int): Seq[(T, Approximate[Long], Boolean)]

    Get the top-k elements.

    Get the top-k elements. Returns sorted in descending order: (item, Approximate[Long], guaranteed)

  23. final def wait(): Unit

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    @throws( ... )

  24. final def wait(arg0: Long, arg1: Int): Unit

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    @throws( ... )

  25. final def wait(arg0: Long): Unit

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