trait CMSHasher[K] extends Serializable
The Count-Min sketch uses d
(aka depth
) pair-wise independent hash functions drawn from a universal
hashing family of the form:
h(x) = [a * x + b (mod p)] (mod m)
As a requirement for using CMS you must provide an implicit CMSHasher[K]
for the type K
of the items
you want to count. Algebird ships with several such implicits for commonly used types K
such as Long
and BigInt
.
If your type K
is not supported out of the box, you have two options: 1) You provide a "translation"
function to convert items of your (unsupported) type K
to a supported type such as Double, and then use
the contramap
function of CMSHasher to create the required CMSHasher[K]
for your type (see the
documentation of contramap
for an example); 2) You implement a CMSHasher[K]
from scratch, using the
existing CMSHasher implementations as a starting point.
- Self Type
- CMSHasher[K]
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- CMSHasher
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Abstract Value Members
- abstract def hash(a: Int, b: Int, width: Int)(x: K): Int
Returns
a * x + b (mod p) (mod width)
.
Concrete Value Members
- final def !=(arg0: Any): Boolean
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- final def ##: Int
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- protected[lang]
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- @throws(classOf[java.lang.CloneNotSupportedException]) @native()
- def contramap[L](f: (L) => K): CMSHasher[L]
Given
f
, a function fromL
intoK
, creates aCMSHasher[L]
whose hash function is equivalent to:Given
f
, a function fromL
intoK
, creates aCMSHasher[L]
whose hash function is equivalent to:def hash(a: Int, b: Int, width: Int)(x: L): CMSHasher[L] = CMSHasher[K].hash(a, b, width)(f(x))
Be aware that the use of contramap may come at a cost (e.g. increased time) due to the translation calls between
K
andL
.Usage
The following example creates a CMSHasher for the unsupported type
K=Double
:def f(d: Double): Array[Byte] = { val l: Long = java.lang.Double.doubleToLongBits(d) java.nio.ByteBuffer.allocate(8).putLong(l).array() } implicit val cmsHasherDouble: CMSHasher[Double] = CMSHasherArrayByte.contramap((d: Double) => f(d))
- final def eq(arg0: AnyRef): Boolean
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- def hashCode(): Int
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- final def notifyAll(): Unit
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- @native()
- def on[L](f: (L) => K): CMSHasher[L]
Given
f
, a function fromL
intoK
, creates aCMSHasher[L]
whose hash function is equivalent to:Given
f
, a function fromL
intoK
, creates aCMSHasher[L]
whose hash function is equivalent to:def hash(a: Int, b: Int, width: Int)(x: L): CMSHasher[L] = CMSHasher[K].hash(a, b, width)(f(x))
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