.NET基类库中是否存在允许使用重复键的字典类?我找到的唯一解决方案是创建,例如,一个类:
Dictionary<string, List<object>>
但实际上用起来很烦人。在Java中,我相信MultiMap可以实现这一点,但在. net中找不到类似的东西。
.NET基类库中是否存在允许使用重复键的字典类?我找到的唯一解决方案是创建,例如,一个类:
Dictionary<string, List<object>>
但实际上用起来很烦人。在Java中,我相信MultiMap可以实现这一点,但在. net中找不到类似的东西。
当前回答
如果同时使用字符串作为键和值,则可以使用System.Collections.Specialized。它将通过GetValues(string key)方法返回一个字符串值数组。
其他回答
这里有一种方法,用List< KeyValuePair< string, string > >
public class ListWithDuplicates : List<KeyValuePair<string, string>>
{
public void Add(string key, string value)
{
var element = new KeyValuePair<string, string>(key, value);
this.Add(element);
}
}
var list = new ListWithDuplicates();
list.Add("k1", "v1");
list.Add("k1", "v2");
list.Add("k1", "v3");
foreach(var item in list)
{
string x = string.format("{0}={1}, ", item.Key, item.Value);
}
输出k1=v1, k1=v2, k1=v3
你可以创建自己的字典包装器,就像这样,作为奖励,它支持空值作为键:
/// <summary>
/// Dictionary which supports duplicates and null entries
/// </summary>
/// <typeparam name="TKey">Type of key</typeparam>
/// <typeparam name="TValue">Type of items</typeparam>
public class OpenDictionary<TKey, TValue>
{
private readonly Lazy<List<TValue>> _nullStorage = new Lazy<List<TValue>>(
() => new List<TValue>());
private readonly Dictionary<TKey, List<TValue>> _innerDictionary =
new Dictionary<TKey, List<TValue>>();
/// <summary>
/// Get all entries
/// </summary>
public IEnumerable<TValue> Values =>
_innerDictionary.Values
.SelectMany(x => x)
.Concat(_nullStorage.Value);
/// <summary>
/// Add an item
/// </summary>
public OpenDictionary<TKey, TValue> Add(TKey key, TValue item)
{
if (ReferenceEquals(key, null))
_nullStorage.Value.Add(item);
else
{
if (!_innerDictionary.ContainsKey(key))
_innerDictionary.Add(key, new List<TValue>());
_innerDictionary[key].Add(item);
}
return this;
}
/// <summary>
/// Remove an entry by key
/// </summary>
public OpenDictionary<TKey, TValue> RemoveEntryByKey(TKey key, TValue entry)
{
if (ReferenceEquals(key, null))
{
int targetIdx = _nullStorage.Value.FindIndex(x => x.Equals(entry));
if (targetIdx < 0)
return this;
_nullStorage.Value.RemoveAt(targetIdx);
}
else
{
if (!_innerDictionary.ContainsKey(key))
return this;
List<TValue> targetChain = _innerDictionary[key];
if (targetChain.Count == 0)
return this;
int targetIdx = targetChain.FindIndex(x => x.Equals(entry));
if (targetIdx < 0)
return this;
targetChain.RemoveAt(targetIdx);
}
return this;
}
/// <summary>
/// Remove all entries by key
/// </summary>
public OpenDictionary<TKey, TValue> RemoveAllEntriesByKey(TKey key)
{
if (ReferenceEquals(key, null))
{
if (_nullStorage.IsValueCreated)
_nullStorage.Value.Clear();
}
else
{
if (_innerDictionary.ContainsKey(key))
_innerDictionary[key].Clear();
}
return this;
}
/// <summary>
/// Try get entries by key
/// </summary>
public bool TryGetEntries(TKey key, out IReadOnlyList<TValue> entries)
{
entries = null;
if (ReferenceEquals(key, null))
{
if (_nullStorage.IsValueCreated)
{
entries = _nullStorage.Value;
return true;
}
else return false;
}
else
{
if (_innerDictionary.ContainsKey(key))
{
entries = _innerDictionary[key];
return true;
}
else return false;
}
}
}
用法示例:
var dictionary = new OpenDictionary<string, int>();
dictionary.Add("1", 1);
// The next line won't throw an exception;
dictionary.Add("1", 2);
dictionary.TryGetEntries("1", out List<int> result);
// result is { 1, 2 }
dictionary.Add(null, 42);
dictionary.Add(null, 24);
dictionary.TryGetEntries(null, out List<int> result);
// result is { 42, 24 }
NameValueCollection支持一个键(也是字符串)下的多个字符串值,但这是我所知道的唯一一个例子。
当我遇到需要这种功能的情况时,我倾向于创建类似于您示例中的结构。
我刚刚遇到了PowerCollections库,其中包括一个名为MultiDictionary的类。它巧妙地包装了这种类型的功能。
我无意中发现了这篇文章,想要寻找相同的答案,但没有找到,所以我使用字典列表构建了一个简单的示例解决方案,当所有其他字典都有给定的键(set)时,重写[]操作符向列表中添加一个新字典,并返回一个值列表(get)。 它既丑陋又低效,它只通过键获取/设置,并且总是返回一个列表,但它是有效的:
class DKD {
List<Dictionary<string, string>> dictionaries;
public DKD(){
dictionaries = new List<Dictionary<string, string>>();}
public object this[string key]{
get{
string temp;
List<string> valueList = new List<string>();
for (int i = 0; i < dictionaries.Count; i++){
dictionaries[i].TryGetValue(key, out temp);
if (temp == key){
valueList.Add(temp);}}
return valueList;}
set{
for (int i = 0; i < dictionaries.Count; i++){
if (dictionaries[i].ContainsKey(key)){
continue;}
else{
dictionaries[i].Add(key,(string) value);
return;}}
dictionaries.Add(new Dictionary<string, string>());
dictionaries.Last()[key] =(string)value;
}
}
}