How can i sort a List of Strings with german umlauts in Dart?

Question

How can is sort a list with umlauts? The compareTo-Function does ignore these an place the word at the end of the list.

main() {
  var fruits = ['Äpfel', 'Bananen', 'Orangen'];
  fruits.sort((a, b) => a.compareTo(b));
}

Answer 1

There is a package called diacritic that make it easy.

https://pub.dev/packages/diacritic

Just put the dependency in pubspec.yml and use it.

dependencies:
  diacritic: ^0.1.1

Import it:

import 'package:diacritic/diacritic.dart';

And use it:

var fruits = ['Äpfel', 'Bananen', 'Orangen'];
fruits.sort((a, b) => removeDiacritics(a).compareTo(removeDiacritics(b)));
print(fruits);

The output will be:

[Äpfel, Bananen, Orangen]

Answer 2

I've created custom comparator based on @DanielJunglas idea. His code wasn't working properly for Polish language and i think it wasn't good for German too. It's for Polish language but can be used in any language, you just need to change letters in map for your alphabet. It ignore's all the other non alphabet sign's. If you want for example to have "+" sign to be compared too and to have it before every other letter just add it to map table with lowest number. If anyone have easier method please tell me. I'm a beginner too.

main() {

var sample = ['Ónda', 'Orangen', 'Ąpfel', 'Okren', 'żarcik', 'Banen', 'Alpa', 'łąka', 'źrebak'];

PolishLettersCompare cmp = new PolishLettersCompare();
  sample.sort(
    (a, b) => cmp.compare(a, b)
  );
}

class PolishLettersCompare {
final Map<String, int> map = {
"A": 1,
"a": 2,
"Ą": 3,
"ą": 4,
"B": 5,
"b": 6,
"C": 7,
"c": 8,
"Ć": 9,
"ć": 10,
"D": 11,
"d": 12,
"E": 13,
"e": 14,
"Ę": 15,
"ę": 16,
"F": 17,
"f": 18,
"G": 19,
"g": 20,
"H": 21,
"h": 22,
"I": 23,
"i": 24,
"J": 25,
"j": 26,
"K": 27,
"k": 28,
"L": 29,
"l": 30,
"Ł": 31,
"ł": 32,
"M": 33,
"m": 34,
"N": 35,
"n": 36,
"Ń": 37,
"ń": 38,
"O": 39,
"o": 40,
"Ó": 41,
"ó": 42,
"P": 43,
"p": 44,
"R": 45,
"r": 46,
"S": 47,
"s": 48,
"Ś": 49,
"ś": 50,
"T": 51,
"t": 52,
"U": 53,
"u": 54,
"V": 55,
"v": 56,
"W": 57,
"w": 58,
"X": 59,
"x": 60,
"Y": 61,
"y": 62,
"Z": 63,
"z": 64,
"Ż": 65,
"ż": 66,
"Ź": 67,
"ź": 68,
};
int charAint;
int charBint;
int compare(String a, String b) {
int min = a.length;
if (b.length < a.length) min = b.length;
for (int i = 0; i < min; ++i) {
  String charA = a[i];
  String charB = b[i];
  if (map.containsKey(charA)) {
    charAint = map[charA];
  }
  if (map.containsKey(charB)) {
    charBint = map[charB];
  }
  if (charAint > charBint)
    return 1;
  else if (charAint < charBint) return -1;
}
if (a.length < b.length)
  return -1;
else if (a.length > b.length) return 1;
return 0;
}
}