CODEWITHSUNDEEP
javalistjava-streammodelmapper
Nitin Kumar
Nitin Kumar

Reputation: 195

Iterate over one collection and get the same index value of another collection

I want know is it even possible in Java to iterate over, let say a list, and get/set the same index(int) value of other list?

for (Response e : responseList) {         
   e.setPrimarySkills(requestList.get(??).getPrimarySkills());
}

Since it can't be done through model mapper because of the issues, is there any neat way of doing the same ?

Upvotes: 2

Views: 615

Answers (5)

M. Justin
M. Justin

Reputation: 21055

One approach is to stream over each index and retrieve the elements pairwise using them:

IntStream.range(0, requestList.size()).forEach(i ->
        responseList.get(i)
                .setPrimarySkills(requestList.get(i).getPrimarySkills()));

Upvotes: 0

M. Justin
M. Justin

Reputation: 21055

Here's a solution using the StreamEx library, zipping the two lists together (pairwise) using zipWith:

StreamEx.of(requestList).zipWith(responseList.stream())
        .forKeyValue((request, response) ->
                response.setPrimarySkills(request.getPrimarySkills()));

Upvotes: 0

Jean Logeart
Jean Logeart

Reputation: 53809

Using two iterators:

Iterator<Response> responseIt = responseList.iterator();
Iterator<Request> requestIt = requestList.iterator();
while(responseIt.hasNext() && requestIt.hasNext()) {
  Response response = responseIt.next();
  Request request = requestIt.next();
  ...
}

[Recommended for its clarity]

Using Guava Streams.forEachPair :

Streams.forEachPair(
  requestList.stream(), 
  responseList.stream(), 
  (req, resp) -> resp.setPrimarySkills(req.getPrimarySkills())
);

Upvotes: 2

Benjamin M
Benjamin M

Reputation: 24527

You can use a for-loop with incrementing index:

List<String> l1 = List.of("a", "b");
List<Integer> l2 = List.of(1, 2);

for(int i=0; i<l1.size(); i++) {
  String s = l1.get(i);
  Integer i = l2.get(i);
}

Of course you should first make sure that both lists have equal length, to avoid OutOfBounds Exception.

Upvotes: 1

Andy Turner
Andy Turner

Reputation: 140299

Either, don't do it with a for-each loop, use an indexed for loop.

for (int i = 0; i < responseList.size(); ++i) {
  responseList.get(i).setPrimarySkills(requestList.get(i).getPrimarySkills());
}

Or, use a pair of Iterators:

Iterator<Response> responseIt = responseList.iterator();
Iterator<Request> requestIt = requestList.iterator();

while (responseIt.hasNext() && requestIt.hasNext()) {
  // Put responseIt.next() and requestIt.next() into variables, if you want.  
responseIt.next().setPrimarySkills(requestIt.next().getPrimarySkills());
}

The advantage of Iterators over an index is that Iterators are efficient for non-RandomAccess lists; but, unless your lists are big, it's unlikely to be a significant (or even noticable) difference.

You can do it with a for-each loop, by maintaining the index yourself, but it's a bit inconsistent in the treatment of the two lists:

int i = 0;
for (Response e : responseList) {         
   e.setPrimarySkills(requestList.get(i).getPrimarySkills());
   i++;
}

Upvotes: 2

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