Displaying list<Map> without duplicates in Dart - list

Question

Suppose I have a List<map> that looks like this:
‘Books’:[
‘B1’{
‘id’: ’1234’,
‘bookName’: ’book1’
},
‘B2’{
‘id’: ’4567’,
‘bookName’: ’book2’
},
‘B3’{
‘id’: ’1234’,
‘bookName’: ’book3’
},
‘B4’{
‘id’: ’8912’,
‘bookName’: ’book4’
},
…
];
I’m trying to return the entire book without duplications in Id.
The expected result should be like this:
‘B1’{
‘id’: ’1234’,
‘bookName’: ’book1’
},
‘B2’{
‘id’: ’4567’,
‘bookName’: ’book2’
},
‘B4’{
‘id’: ’8912’,
‘bookName’: ’book4’
},

Answer 1

I guessed what your input map was and made a solution based on this answer from Basic Coder.
final list = {
'Books':[
{
'id':'1234',
'bookName':'book1'
},
{
'id':'4567',
'bookName':'book2'
},
{
'id': '1234',
'bookName':'book3'
},
{
'id': '8912',
'bookName':'book4'
},
]};
void main() {
print('With duplicates $list');
final ids = list['Books']!.map<String>((e) => e['id']!).toSet();
list['Books']!.retainWhere((Map x) {
return ids.remove(x['id']);
});
print('Without duplicates $list');
}
This code shows your input as the variable list, which seems to be what you were going for with your provided data. The code then obtains a list of each id of the book and removes duplicates by changing it to a Set. Then it only retains elements in the original list with those non-duplicate ids.
Remove the ! operators if you're not using null-safety.

Answer 2

Here's one inspired by Christopher's answer:
void main() {
var books = {
'B1': {
'id': '1234',
'bookName': 'book1',
},
'B2': {
'id': '4567',
'bookName': 'book2',
},
'B3': {'id': '1234', 'bookName': 'book3'},
'B4': {'id': '8912', 'bookName': 'book4'},
};
var seen = <String>{};
var kept = books.entries.where((me) => seen.add(me.value['id'] ?? 'OTHER'));
print(Map.fromEntries(kept));
}
I think it's a bit simpler, since it doesn't have to populate the Set first. I also learned that Set.add returns a bool to indicate the element didn't exist before. Nice.