Elegant way of doing ruby inject in Java 8

Question

String result = "";
for(String str : strings) {
    result = apply(result, str);
}
return result;

I want to pass through the result of one operation with next element in the loop. Is there any elegant way of doing this in Java 8?

For example, in Ruby, we can use inject.

strings.inject("") { |s1, s2| apply(s1,s2) }

score 9 · Accepted Answer · edited Dec 08 '15 at 18:35

9

You can use reduce :

String result = strings.stream().reduce("", this::apply);

edited Dec 08 '15 at 18:35

nickb

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answered Dec 08 '15 at 18:32

Mrinal

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Note: `inject` is also called `reduce` in Ruby. https://stackoverflow.com/questions/13813243/is-inject-the-same-thing-as-reduce-in-ruby – Eric Duminil Jul 20 '19 at 08:23

Donald Raab · Answer 2 · 2017-05-26T05:22:32.050

If you don't mind adding a third-party library, you could use Eclipse Collections which has injectInto methods on its object and primitive containers. Eclipse Collections was inspired by the Smalltalk Collections API which also inspired Ruby. Here are some examples of using object (mutable and immutable) and primitive (mutable and immutable) containers with injectInto.

@Test
public void inject()
{
    MutableList<String> strings1 = Lists.mutable.with("1", "2", "3");
    Assert.assertEquals("123", strings1.injectInto("", this::apply));

    ImmutableList<String> strings2 = Lists.immutable.with("1", "2", "3");
    Assert.assertEquals("123", strings2.injectInto("", this::apply));

    IntList ints = IntLists.mutable.with(1, 2, 3);
    Assert.assertEquals("123", ints.injectInto("", this::applyInt));

    LazyIterable<Integer> boxedInterval = Interval.oneTo(3);
    Assert.assertEquals("123", boxedInterval.injectInto("", this::applyInt));

    IntList primitiveInterval = IntInterval.oneTo(3);
    Assert.assertEquals("123", primitiveInterval.injectInto("", this::applyInt));
}

public String apply(String result, String each)
{
    return result + each;
}

public String applyInt(String result, int each)
{
    return result + each;
}

Note: I am a committer for Eclipse Collections

Elegant way of doing ruby inject in Java 8

2 Answers2