Munging data streams with functional programming and lambda expressions in Java 8

Tue, 16 May 2017 23:59:39 +0000

With the advent of Java 8 and java.util.stream and lambda expressions in it, one can do data munging in Java 8 as the following:

Java 8:

public static void main(String[] args) {

    HashMap<Integer, Character> nucleobases = new HashMap<> ();
    nucleobases.put(1, 'A');
    nucleobases.put(2, 'G');
    nucleobases.put(3, 'T');
    nucleobases.put(4, 'C');


    range(0, 100)
            // generate a stream containing random strings of length 10
            .mapToObj(i -> randomNucleicAcidSequence(new Random(), nucleobases, 10))
            // sort the elements in the stream to natural ordering
            .sorted()
            // group strings into sub-lists and wrap them into a stream
            .collect(groupingBy(name -> name.charAt(0)))
            // print each sub-list's common initial letter and the constituent strings
            .forEach((letter, names) -> System.out.println(letter
                    + "\n\t"
                    + names.stream().collect(joining("\n\t"))));
}

public static String randomNucleicAcidSequence(Random r, Map<Integer, Character> map, int length) {
    return r.ints(1, 4).limit(length).mapToObj(
            x -> Character.toString(map.get(x))).collect(Collectors.joining());
}

↑ Code in GitHub

This is remarkbly similar to a program written in Mathematica using the munging style I use all the time:

(* There is not a built-in RandomString[…] *)
nucleobases = {"A", "G", "T", "C"};

randomNucleicAcidSequence[length_Integer] := StringJoin[nucleobases[[#]] & /@ RandomInteger[{1, 4}, length]]

Composition[
    Print[StringJoin[{#[[1]],":\n",StringJoin[Riffle[#[[2]],"\n"]]}]]& /@ # &,
    (First[Characters[Part[#, 1]]]-> #) & /@ # &,
    GatherBy[#, First[Characters[#]]&]&,
    Sort,
    Map[Function[{i}, randomNucleicAcidSequence[10]], #] &
][Range[0, 100]]

The output of both program print the mucleic acid sequences grouped by initial neuclobase:

A:
AAAATACCTC
AAATAATCAT
AACAGATACG
ACAACTACGG
ACCATCAAAT
...
C:
CAACGGGGTT
CAAGAAGAGC
CACACCCACA
CACACTCTAC
CAGGACCGGA
...
G:
GAACGTTTCA
GAACTAAGCG
GACCAGTTCT
GAGAACACGT
GAGCCGCCAC
...
T:
TAAAATTGCC
TAAGGTGAGG
TAGCCGGTTA
TAGGCGGTGA
TAGTTCGAGC
...

Data streams and algorithms for processing them is a recently hot research area in computer science. It seems to me it will be natural for Java standard library to include more and more stream algorithms in future.

Munging style for Mathematica code layout

pages tagged functional_programming

Munging data streams with functional programming and lambda expressions in Java 8