Remove duplicate items from array based on some attribute value

Question

I have a list, unfilteredList, with 12 items (messages). As seen in the output, 9 of these messages have the same roomID. My question is then: How can I filter away 8 of these 9 items, such that my list, result, only has 1 of each roomIDs?

I've tried to mess about with for loops and remove an item whenever a second roomID is met. But can't seem to get it working, what am I doing wrong?

List <Inbox> result = [];
int count = 0;
for(int i = 0; i < unfilteredList.length; i++){

  print(i.toString() + '. roomID: ' + unfilteredList[i].roomId);

  result.add(blah[i]);

  for(int j = 0; j < result.length; j++){
    if(result[j].roomId == unfilteredList[i].roomId){
      count++;
      if(count > 1){
        result.removeLast();
        count--;
      }
    }
  }
}

Output from print:

I/flutter (15029): 0. roomID: 1206f5058913246b47f898e7ab7e41ad
I/flutter (15029): 1. roomID: 15b08ee59f29b43d21a24ea6d4071b19
I/flutter (15029): 2. roomID: cd674af0f6048af49bf8222f24bd6103
I/flutter (15029): 3. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 4. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 5. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 6. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 7. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 8. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 9. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 10. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 11. roomID: e5e210a53a3c7e1b03d6cbedbc9da786
I/flutter (15029): 12. roomID: f3f1e4385b36cdd04e10e776220b892e

Mobina · Accepted Answer · 2020-08-27 15:29:12Z

1

You can use a Set to store the unique roomIds. Each time a new id is being added to the set, remove it from the result list if the set already includes it.

final uniqueIds = Set<String>();
result.removeWhere((item) => !uniqueIds.add(item.roomId));

answered Aug 27, 2020 at 15:29

Mobina

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Comments

Marcel Dz · Accepted Answer · 2020-08-27 12:23:22Z

0

Well you can just check for the id with .contains() see an output from one of my apps as example:

for (var idx = 0; idx < sampleList.length; idx++){
      if(result.contains(sampleList[idx].userId)){
        print('id exists');
      } else {
        result.add(sampleList[idx].userId);
      }    
    }

It would add the id e5e210a53a3c7e1b03d6cbedbc9da786 the first time and after that skip it.

answered Aug 27, 2020 at 12:23

Marcel Dz

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2 Comments

jeffmayn Over a year ago

This was my first attempt actually. Does not work :( Think its because I need "result.add(unfilteredList[i]);" in the else-clause and not "result.add(unfilteredList[i].roomID)"

jeffmayn Over a year ago

So I can't really use .containts() in my case, I think :/

HBS · Accepted Answer · 2020-08-27 14:49:00Z

0

Use toSet() and then toList().

final uniqueList = results.toSet().toList();

answered Aug 27, 2020 at 14:49

HBS

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