Packages

c

com.twitter.algebird

SemigroupCombinator

class SemigroupCombinator[A, B] extends Semigroup[(A, B)]

This is a combinator on semigroups, after you do the plus, you transform B with a fold function This will not be valid for all fold functions. You need to prove that it is still associative.

Clearly only values of (a,b) are valid if fold(a,b) == b, so keep that in mind.

I have not yet found a sufficient condition on (A,B) => B that makes it correct Clearly a (trivial) constant function {(l,r) => r} works. Also, if B is List[T], and (l:A,r:List[T]) = r.sortBy(fn(l)) this works as well (due to the associativity on A, and the fact that the list never loses data).

For approximate lists (like top-K applications) this might work (or be close enough to associative that for approximation algorithms it is fine), and in fact, that is the main motivation of this code: Produce some ordering in A, and use it to do sorted-topK on the list in B.

Seems like an open topic here.... you are obliged to think on your own about this.

Linear Supertypes
Semigroup[(A, B)], AdditiveSemigroup[(A, B)], cats.kernel.Semigroup[(A, B)], Serializable, AnyRef, Any
Known Subclasses
MonoidCombinator
Ordering
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Inherited
  1. SemigroupCombinator
  2. Semigroup
  3. AdditiveSemigroup
  4. Semigroup
  5. Serializable
  6. AnyRef
  7. Any
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Visibility
  1. Public
  2. Protected

Instance Constructors

  1. new SemigroupCombinator(fold: (A, B) => B)(implicit arg0: Semigroup[A], arg1: Semigroup[B])

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##: Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. def additive: algebra.Semigroup[(A, B)]
    Definition Classes
    Semigroup → AdditiveSemigroup
  5. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  6. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.CloneNotSupportedException]) @native()
  7. def combine(l: (A, B), r: (A, B)): (A, B)
    Definition Classes
    Semigroup → Semigroup
  8. def combineAllOption(iter: TraversableOnce[(A, B)]): Option[(A, B)]
    Definition Classes
    Semigroup → Semigroup
  9. def combineN(a: (A, B), n: Int): (A, B)
    Definition Classes
    Semigroup
  10. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  11. def equals(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef → Any
  12. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.Throwable])
  13. final def getClass(): Class[_ <: AnyRef]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  14. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  15. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  16. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  17. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  18. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  19. def plus(left: (A, B), right: (A, B)): (A, B)
    Definition Classes
    SemigroupCombinator → AdditiveSemigroup
  20. def positiveSumN(a: (A, B), n: Int): (A, B)
    Attributes
    protected[this]
    Definition Classes
    AdditiveSemigroup
  21. def repeatedCombineN(a: (A, B), n: Int): (A, B)
    Attributes
    protected[this]
    Definition Classes
    Semigroup
  22. def sumN(a: (A, B), n: Int): (A, B)
    Definition Classes
    AdditiveSemigroup
  23. def sumOption(iter: TraversableOnce[(A, B)]): Option[(A, B)]

    Returns an instance of T calculated by summing all instances in iter in one pass.

    Returns an instance of T calculated by summing all instances in iter in one pass. Returns None if iter is empty, else Some[T].

    iter

    instances of T to be combined

    returns

    None if iter is empty, else an option value containing the summed T

    Definition Classes
    Semigroup
    Note

    Override if there is a faster way to compute this sum than iter.reduceLeftOption using plus.

  24. final def synchronized[T0](arg0: => T0): T0
    Definition Classes
    AnyRef
  25. def toString(): String
    Definition Classes
    AnyRef → Any
  26. def trySum(iter: TraversableOnce[(A, B)]): Option[(A, B)]
    Definition Classes
    Semigroup → AdditiveSemigroup
  27. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  28. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  29. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException]) @native()

Inherited from Semigroup[(A, B)]

Inherited from AdditiveSemigroup[(A, B)]

Inherited from cats.kernel.Semigroup[(A, B)]

Inherited from Serializable

Inherited from AnyRef

Inherited from Any

Ungrouped