Stream of String Array to a Json or Hashmap

I have a stream of string arrays and each has a length of two. I would like to convert it into a json after the stream . The first element in the string array is a sort of a key and the second one of its possible values. How can I covert it ?

Input Stream: [c1 , 1234] , [c1, 3434] , [c2 , 887],[c1 , 52] , [c1 , 372],[c2 ,7292], [c3 , 302]..

Output

   {
     "c1" : [1234, 3434, 52,372],
     "c2" : [887, 7292]
     "c3" : [302]
}

It makes most sense to do it like this:

List<String[]> list = new ArrayList<String[]>();
list.add(new String[] { "c1", "1234" });
list.add(new String[] { "c1", "3434" });
list.add(new String[] { "c2", "887" });
list.add(new String[] { "c1", "52" });
list.add(new String[] { "c1", "372" });
list.add(new String[] { "c2", "7292" });
list.add(new String[] { "c2", "302" });
Map<String, Set<String>> map = list.stream().collect(
Collectors.toMap(t -> t[0], t -> new HashSet<String>(Arrays.asList(new String[] { t[1] })), (t, u) -> {
t.addAll(u);
return t;
}));

But I'm a bit obsessive about one-liners, so I like to do it like this:

Map<String, Set<String>> map = list.stream()
.collect(Collectors.toMap(t -> t[0],
t -> (Set<String>) new HashSet<String>(Arrays.asList(new String[] { t[1] })),
(t, u) -> Stream.concat(t.stream(), u.stream()).collect(Collectors.toSet())));

Either way, this is the output:

{
"c1": [
"1234",
"3434",
"52",
"372"
],
"c2": [
"302",
"887",
"7292"
]
}

This should get you started.

• split the string int Cn ### pairs
• and convert to a map using Cn as the key and a list of ### as the value.

String str =
"[c1 , 1234] , [c1, 3434] , [c2 , 887],[c1 , 52] , [c1 , 372],[c2 ,7292], [c3 , 302]";
String[] arr = str.replaceAll("[\\[\\]\\s]", "").split(",");
Map<String, List<Integer>> map = 
IntStream.iterate(0, i -> i < arr.length, i -> i + 2)
.mapToObj(i -> new String[] { arr[i], arr[i + 1] })
.collect(Collectors.groupingBy(a -> a[0],
TreeMap::new,
Collectors.mapping(
a -> Integer.parseInt(a[1]),
Collectors.toList())));
StringBuilder sb = new StringBuilder("{\n");
map.forEach((k, v) -> sb.append(
"  \"" + k + "\"" + " : " + v.toString() + ",\n"));
int comma = sb.lastIndexOf(",");
sb.replace(comma, comma + 1, "\n}");
System.out.println(sb);

Prints

{
"c1" : [1234, 3434, 52, 372],
"c2" : [887, 7292],
"c3" : [302]
}
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