How to sort map's values?

问题:

Can someone give me a hint? I want to sort a map's values by the length of the lists.

var chordtypes = {
  "maj": [0, 4, 7],
  "M7": [0, 4, 7, 11],
  "m7": [0, 3, 7, 10],
  "6": [0, 4, 7, 9],
  "9": [0, 4, 7, 10, 14],
  "sus2": [0, 2, 7],
  "sus4": [0, 5, 7],
  "omit3": [0, 7],
  "#5": [0, 4, 8],
  "+7b9#11": [0, 4, 8, 10, 13, 18],
  "+9": [0, 4, 8, 10, 14]
};

回答1:

A function that does sort a Map of List on their length.

import 'dart:collection';

/// sorts the ListMap (== A Map of List<V>) on the length
/// of the List values.
LinkedHashMap sortListMap(LinkedHashMap map) {
    List mapKeys = map.keys.toList(growable : false);
    mapKeys.sort((k1, k2) => map[k1].length - map[k2].length);
    LinkedHashMap resMap = new LinkedHashMap();
    mapKeys.forEach((k1) { resMap[k1] = map[k1] ; }) ;        
    return resMap;
}

result for :

var res = sortListMap(chordtypes);
print(res);

==>

{ omit3: [0, 7], 
  maj: [0, 4, 7], 
  sus2: [0, 2, 7], 
  sus4: [0, 5, 7], 
  #5: [0, 4, 8], 
  M7: [0, 4, 7, 11], 
  m7: [0, 3, 7, 10], 
  6: [0, 4, 7, 9], 
  9: [0, 4, 7, 10, 14], 
  +9: [0, 4, 8, 10, 14], 
  +7b9#11: [0, 4, 8, 10, 13, 18] }

回答2:

Something like this could work for you:

Map chordtypes = {
  "maj": [0, 4, 7],
  "M7": [0, 4, 7, 11],
  "m7": [0, 3, 7, 10],
  "6": [0, 4, 7, 9],
  "9": [0, 4, 7, 10, 14],
  "sus2": [0, 2, 7],
  "sus4": [0, 5, 7],
  "omit3": [0, 7],
  "#5": [0, 4, 8],
  "+7b9#11": [0, 4, 8, 10, 13, 18],
  "+9": [0, 4, 8, 10, 14]
};

List keys = chordtypes.keys.toList();
keys.sort((k1, k2) {
  if(chordtypes[k1].length > chordtypes[k2].length)
    return -1;
  if(chordtypes[k1].length < chordtypes[k2].length)
    return 1;
  return 0;
});
keys.forEach((String k) {
  print('$k ${chordtypes[k]}');
});

回答3:

import "package:queries/collections.dart";

void main() {
  var chordtypes = {
    "maj": [0, 4, 7],
    "M7": [0, 4, 7, 11],
    "m7": [0, 3, 7, 10],
    "6": [0, 4, 7, 9],
    "9": [0, 4, 7, 10, 14],
    "sus2": [0, 2, 7],
    "sus4": [0, 5, 7],
    "omit3": [0, 7],
    "#5": [0, 4, 8],
    "+7b9#11": [0, 4, 8, 10, 13, 18],
    "+9": [0, 4, 8, 10, 14]
  };

  var dict = new Dictionary<String, List>.fromMap(chordtypes);
  // Sort by list length, then by key
  var sorted = dict
      .orderBy((kv) => kv.value, (a, b) => b.length.compareTo(a.length))
      .thenBy((kv) => kv.key, (a, b) => a.compareTo(b));
  dict = sorted.toDictionary((kv) => kv.key, (kv) => kv.value);
  for (var kv in dict) {
    print("$kv");
  }
}

Sorted by [listLength, key]

+7b9#11 : [0, 4, 8, 10, 13, 18]
+9 : [0, 4, 8, 10, 14]
9 : [0, 4, 7, 10, 14]
6 : [0, 4, 7, 9]
M7 : [0, 4, 7, 11]
m7 : [0, 3, 7, 10]
#5 : [0, 4, 8]
maj : [0, 4, 7]
sus2 : [0, 2, 7]
sus4 : [0, 5, 7]
omit3 : [0, 7]