Package com.singularsys.extensions.stream

Class StreamFunctionSet

java.lang.Object
com.singularsys.jep.misc.OneShotComponent
com.singularsys.jep.misc.FunctionSet
com.singularsys.extensions.stream.StreamFunctionSet
All Implemented Interfaces:
JepComponent, Serializable
public class StreamFunctionSet extends FunctionSet
Adds stream processing functions.
  • Generators:
    • iterate - creates a stream using an initial value, a unary lambda function giving the next value and an optional predicate lambda function to determine when to end the stream. iterate(0, x=>x+1, x=>x<10) . count() or iterate(1, x=>x*2) . limit(10) . toList()
  • Intermediate functions:
    • map - maps a stream using a lambda function: [1..5] . map(x=>x*x)
    • filter - filters a stream using a lambda function a predicate: [1..10] . filter(x=>x%2==0)
    • accumulate - accumulate value of sequence, returning a stream of intermediate values: [1..5] . accumulate(0,[tot,val]=>tot+val) produces [1,3,6,10,15]
    • sort - sorts a stream by a lambda function: [3,1,4,2] . sort((a,b)=>a>b)
    • dsort - sorts a stream by numeric value: [3,1,4,2] . dsort()
    • rsort - sorts a stream by reverse numeric value: [3,1,4,2] . rsort()
    • limit - limits a stream to a number of elements: [1..100] . limit(10)
    • skip - skips a number of elements in a stream: [1..100] . skip(90)
    • while - takes elements from a stream while a predicate is true: [1..100] . while(x=>x<10)
    • append - concatenates two streams together: [1..5] . append([6..10])
    • merge - merge two streams together pairwise using a lambda function to define how to merge elements: [1..5] . merge((a,b)=>a+b, [6..10])
    • loop - loops a stream indefinitely: [1..5] . loop() . limit(12) produces [1,2,3,4,5,1,2,3,4,5,1,2]
    • distinct - return a stream with duplicate elements removed: [1,2,3,2,1] . distinct() produces [1,2,3] order is not guaranteed.
  • Terminal functions:
    • fold - folds a stream using a binary lambda function: [1..5]. fold((a,b)=>a+b)
    • foldOr - folds a stream using a binary lambda function, returning a default value if the stream is empty [1..5] . foldOr((a,b)=>a+b, -1)
    • reduce - reduces a stream using a binary lambda function and an initial value [1..5] . reduce(1, (a,b)=>a*b)
    • first - returns the first element of a stream [1..5] . first()
    • firstOr - returns the first element of a stream or a default value if the stream is empty [1..5] . firstOr(-1)
    • last - returns the last element of a stream [1..5] . last()
    • count - counts the number of elements in a stream [1..5] . count()
    • min - finds the minimum numeric value of a stream: [1..5] . min()
    • max - finds the maximum numeric value of a stream: [1..5] . max()
    • toList - turns a stream into a Jep list [1..5] . toList()
    • anyMatch - returns true if any item match a predicate [1..5] . anyMatch(x => x%2==0)
    • allMatch - returns true if all items match a predicate [1..5] . allMatch(x => x%2==0)
    • noneMatch - returns true if no items match a predicate [1..5] . noneMatch(x => x%2==0)
    • firstMatchOr - finds the first matching item or a default value [1..5] . firstMatchOr(x => x%2==0, -1)
  • Other functions:
    • apply - applies a lambda function, treating the input as a single variable, converting the input streams to lists. [1..10] . map(x=>x^2) . apply(v=>avg(v)) . apply(x=>sqrt(x))
    • chained - applies a lambda function, treating the input as a single variable [1..5] . chained(seq => seq . map(x=>x^2)) .sum()
    • define - defines regular Jep function using a lambda function: define(mysum, [x,y] => x+y); mysum(2,3);
    • clone - clone a stream so multiple copies can be used within a lambda function: [1..5] . chained(seq => clone(seq) . append(clone(seq)))
    • car - get the first element of a stream
    • clone - get a stream with the first element removed: [3..7] . chained(seq=>[car(seq),cdr(seq)])

These functions can either be used in a chain, e.g. [1..10] . filter(x=>x%2==0) . map(x=>x*x) . toList() or with the stream as an argument, e.g. filter(x=>x%2==0,[1..10]) . For most functions the preceding item in the chain becomes the last item in the argument list. So [1..10] .reduce(1, (a,b)=>a*b) is the same as reduce(1, (a,b)=>a*b, [1..10]) . There are two exceptions

  • append - [1..5] . append([6..10]) is the same as append([1..5], [6..10])
  • merge - [1..5] . merge((a,b)=>a+b, [6..10]) is the same as merge((a,b)=>a+b, [1..5], [6..10])
as the swapped versions are semantically more intuitive.

Names used can be changed in the properties file com.singularsys.extensions.messages.properties 

StreamFunctionSet.map = map
Use an ! in the property value to prevent the function being added, e.g. 
StreamFunctionSet.map = !skip
Since:
Jep 4.1 extensions 2.2
See Also:

  • Constructor Details

    • StreamFunctionSet

      public StreamFunctionSet()
      Creates a set of stream enabled higher order functions. The implementations uses Double.compareTo(Double) to compare numeric values in the nsort and rsort functions; StreamMinMax to find the minimum and maximum numeric values in the min and max functions; and Add to sum numeric values in the sum function.

    • StreamFunctionSet

      public StreamFunctionSet(FieldI field)
      Creates a set of stream enable higher order functions for a specific field. The implementations uses FieldComparator in the nsort and rsort functions; ElementMinMax to find the minimum and maximum numeric values in the min and max functions; and the FieldI.add(Object, Object) method to sum numeric values in the sum function.
      Parameters:
      field - Field to use for numeric comparisons and sums.