+
+Package org.apache.datasketches.sampling
+Class EbppsItemsSketch<T>
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- java.lang.Object +
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- org.apache.datasketches.sampling.EbppsItemsSketch<T> +
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+public class EbppsItemsSketch<T> +extends Object
+An implementation of an Exact and Bounded Sampling Proportional to Size sketch. + + From: "Exact PPS Sampling with Bounded Sample Size", + B. Hentschel, P. J. Haas, Y. Tian. Information Processing Letters, 2023. + + This sketch samples data from a stream of items proportional to the weight of each item. + The sample guarantees the presence of an item in the result is proportional to that item's + portion of the total weight seen by the sketch, and returns a sample no larger than size k. + + The sample may be smaller than k and the resulting size of the sample potentially includes + a probabilistic component, meaning the resulting sample size is not always constant.+-
+
- Author: +
- Jon Malkin +
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Constructor Summary
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+Constructors ++ +Constructor +Description ++ +EbppsItemsSketch(int k)+ +Constructor+
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Method Summary
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+ +All Methods Static Methods Instance Methods Concrete Methods ++ +Modifier and Type +Method +Description ++ +doublegetC()+ +Returns the expected number of samples returned upon a call to + getResult().++ +doublegetCumulativeWeight()+ +Returns the cumulative weight of items processed by the sketch.++ +intgetK()+ +Returns the configured maximum sample size.++ +longgetN()+ +Returns the number of items processed by the sketch, regardless + of item weight.++ +ArrayList<T>getResult()+ +Returns a copy of the current sample.++ +intgetSerializedSizeBytes(ArrayOfItemsSerDe<? super T> serDe)+ +Returns the size of a byte array representation of this sketch.++ +intgetSerializedSizeBytes(ArrayOfItemsSerDe<? super T> serDe, + Class<?> clazz)+ +Returns the length of a byte array representation of this sketch.++ +static <T> EbppsItemsSketch<T>heapify(org.apache.datasketches.memory.Memory srcMem, + ArrayOfItemsSerDe<T> serDe)+ +Returns a sketch instance of this class from the given srcMem, + which must be a Memory representation of this sketch class.++ +booleanisEmpty()+ +Returns true if the sketch is empty.++ +voidmerge(EbppsItemsSketch<T> other)+ +Merges the provided sketch into the current one.++ +voidreset()+ +Resets the sketch to its default, empty state.++ +byte[]toByteArray(ArrayOfItemsSerDe<? super T> serDe)+ +Returns a byte array representation of this sketch.++ +byte[]toByteArray(ArrayOfItemsSerDe<? super T> serDe, + Class<?> clazz)+ +Returns a byte array representation of this sketch.++ +StringtoString()+ +Provides a human-readable summary of the sketch++ +voidupdate(T item)+ +Updates this sketch with the given data item with weight 1.0.++ +voidupdate(T item, + double weight)+ +Updates this sketch with the given data item with the given weight.+
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Method Detail
+ + + +-
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heapify
+public static <T> EbppsItemsSketch<T> heapify(org.apache.datasketches.memory.Memory srcMem, + ArrayOfItemsSerDe<T> serDe)
+Returns a sketch instance of this class from the given srcMem, + which must be a Memory representation of this sketch class.+-
+
- Type Parameters: +
T- The type of item this sketch contains
+- Parameters: +
srcMem- a Memory representation of a sketch of this class. + See Memory
+serDe- An instance of ArrayOfItemsSerDe
+- Returns: +
- a sketch instance of this class +
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update
+public void update(T item)
+Updates this sketch with the given data item with weight 1.0.+-
+
- Parameters: +
item- an item from a stream of items
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update
+public void update(T item, + double weight)
+Updates this sketch with the given data item with the given weight.+-
+
- Parameters: +
item- an item from a stream of items
+weight- the weight of the item
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merge
+public void merge(EbppsItemsSketch<T> other)
+Merges the provided sketch into the current one.+-
+
- Parameters: +
other- the sketch to merge into the current object
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getResult
+public ArrayList<T> getResult()
+Returns a copy of the current sample. The exact size may be + probabilsitic, differing by at most 1 item.+-
+
- Returns: +
- the current sketch sample +
+
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toString
+public String toString()
+Provides a human-readable summary of the sketch+ +
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getK
+public int getK()
+Returns the configured maximum sample size.+-
+
- Returns: +
- configured maximum sample size +
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getN
+public long getN()
+Returns the number of items processed by the sketch, regardless + of item weight.+-
+
- Returns: +
- count of items processed by the sketch +
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getCumulativeWeight
+public double getCumulativeWeight()
+Returns the cumulative weight of items processed by the sketch.+-
+
- Returns: +
- cumulative weight of items seen +
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getC
+public double getC()
+Returns the expected number of samples returned upon a call to + getResult(). The number is a floating point value, where the + fractional portion represents the probability of including a + "partial item" from the sample. + + The value C should be no larger than the sketch's configured + value of k, although numerical precision limitations mean it + may exceed k by double precision floating point error margins + in certain cases.+-
+
- Returns: +
- The expected number of samples returned when querying the sketch +
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isEmpty
+public boolean isEmpty()
+Returns true if the sketch is empty.+-
+
- Returns: +
- empty flag +
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reset
+public void reset()
+Resets the sketch to its default, empty state.+
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getSerializedSizeBytes
+public int getSerializedSizeBytes(ArrayOfItemsSerDe<? super T> serDe)
+Returns the size of a byte array representation of this sketch. May fail for polymorphic item types.+-
+
- Parameters: +
serDe- An instance of ArrayOfItemsSerDe
+- Returns: +
- the length of a byte array representation of this sketch +
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getSerializedSizeBytes
+public int getSerializedSizeBytes(ArrayOfItemsSerDe<? super T> serDe, + Class<?> clazz)
+Returns the length of a byte array representation of this sketch. Copies contents into an array of the + specified class for serialization to allow for polymorphic types.+-
+
- Parameters: +
serDe- An instance of ArrayOfItemsSerDe
+clazz- The class represented by <T>
+- Returns: +
- the length of a byte array representation of this sketch +
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toByteArray
+public byte[] toByteArray(ArrayOfItemsSerDe<? super T> serDe)
+Returns a byte array representation of this sketch. May fail for polymorphic item types.+-
+
- Parameters: +
serDe- An instance of ArrayOfItemsSerDe
+- Returns: +
- a byte array representation of this sketch +
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toByteArray
+public byte[] toByteArray(ArrayOfItemsSerDe<? super T> serDe, + Class<?> clazz)
+Returns a byte array representation of this sketch. Copies contents into an array of the + specified class for serialization to allow for polymorphic types.+-
+
- Parameters: +
serDe- An instance of ArrayOfItemsSerDe
+clazz- The class represented by <T>
+- Returns: +
- a byte array representation of this sketch +
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