Convert String[] str = {"a","b","c","d","e","f"} to map like {a=b, c=d, e=f} using java stream

Question

I have the below code to implement the requirement, but couldn't solve using stream , I'm not sure how to increment i in pipeline

String[] str = {"a","b","c","d","e","f"};
    Map<String, String> strMap = new HashMap<>();
    int i = 0;
    while(i< str.length && i +1 < str.length) {
        strMap.put(str[i],str[i+1]);
        i +=2;          
    }

If you can use Guava https://stackoverflow.com/questions/9489384/initializing-a-guava-immutablemap — dehasi, Oct 17 '17 at 17:16

score 4 · Answer 1 · edited Oct 17 '17 at 02:31

4

You can't do it with a simple stream of str, but you can mimic your loop with an index stream:

Map<String, String> strMap = IntStream.range(0, str.length - 1)
        .filter(i -> i % 2 == 0)
        .boxed()
        .collect(Collectors.toMap(i -> str[i], i -> str[i + 1]));

edited Oct 17 '17 at 02:31

Naman

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answered Oct 17 '17 at 01:02

shmosel

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Thanks ! very helpful – prisesh Oct 17 '17 at 02:51

score 3 · Accepted Answer · answered Oct 17 '17 at 01:01

3

It's a bit of a hack, but you could use an IntStream to generate your indices (between 0 and the length of the array), filter out the odd indices and then use a forEach to populate the strMap - like,

String[] str = { "a", "b", "c", "d", "e", "f" };
Map<String, String> strMap = new HashMap<>();
IntStream.range(0, str.length).filter(i -> i % 2 == 0)
        .forEach(i -> strMap.put(str[i], str[i + 1]));
System.out.println(strMap);

Which outputs (as requested)

{a=b, c=d, e=f}

answered Oct 17 '17 at 01:01

Elliott Frisch

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Thanks! solved my problem :) – prisesh Oct 17 '17 at 02:51
1

Or `IntStream.range(0, str.length/2).map(i -> i*2)` which performs less operations, but on the other hand, won’t fail-fast when the array has an odd length. – Holger Oct 17 '17 at 06:40
@Holger OP's version doesn't fail on odd length either. – shmosel Oct 17 '17 at 16:54
@shmosel: but I consider failing for malformed input a good thing. – Holger Oct 18 '17 at 06:20
@Holger I would generally agree, but it's hard to declare it malformed without more context. – shmosel Oct 18 '17 at 06:21

Convert String[] str = {"a","b","c","d","e","f"} to map like {a=b, c=d, e=f} using java stream

2 Answers2