delete duplicates from a list in dart - flutter

Question

hey there i am trying to display all of the options from my database in a dropdown,i have them displaying but i only want one of each result to appear and i cant figure out how to to get ride of the duplicates this is what it looks like when i click on the dropdown
here is the code to pull in the results
void _getFieldsData() {
getUserDetails().then((data) {
final items = jsonDecode(data).cast<Map<String, dynamic>>();
var fieldListData = items.map<User>((json) {
return User.fromJson(json);
}).toSet().toList();
///set list for class
_selectedField = fieldListData[0].series;
_selectedField = fieldListData[0].classs;
setState(() {
for (Map user in items) {
_userDetails.add(User.fromJson(user));
print(_userDetails.length);
//if (_userDetails.classs != userDetail.classs.contains(_selectedText))
}
});
// update widget
setState(() {
_fieldList = fieldListData.toSet().toList();
//print(resultseries);
// print(uniqueCount);
print(_fieldList);
});
});
here is the dropdown
new DropdownButton<String>(
hint: Text("Series"),
// value: null,
items: _fieldList.map((value){
return DropdownMenuItem<String>(
value: value.series,
child: Container(
width: 100,
child: new Text(value.series),

Answer 1

it's not clear exactly what your User class looks like, but im assuming you have multiple fields that do not all have same values, for example, each with a unique id, that's why the following line isn't working in your case:
setState(() {
_fieldList = fieldListData.toSet().toList();
});
i would suggest using List.fold, List.any, and change the line above to check for only .series field, as below:
List initialResultsList = [];
setState(() {
// use fold (similar to .reduce()) to iterate through fieldListData and return the updated filtered 'results'
// list with each iteration:
_fieldList = fieldListData.fold(initialResultsList, (results, currentItem) {
// check to see if currentItem.series already exists in any item of filtered results:
if (!results.any((item) => item.series == currentItem.series)) {
// if not, add it to results:
results.add(currentItem);
}
// return results for next iteration
return results;
});
}