我有一个Person对象列表。我想转换为Dictionary，其中键是第一个和最后一个名字(连接)，值是Person对象。
问题是我有一些重复的人，所以这爆炸如果我使用以下代码:
private Dictionary<string, Person> _people = new Dictionary<string, Person>();
_people = personList.ToDictionary(
e => e.FirstandLastName,
StringComparer.OrdinalIgnoreCase);
我知道这听起来很奇怪，但我现在真的不关心重复的名字。如果有多个名字，我只想取一个。有没有什么方法可以让上面的代码只取其中一个名字而不会重复?
当前回答
使用LINQ等效的foldLeft功能
persons.Aggregate(new Dictionary<string,Person>(StringComparer.OrdinalIgnoreCase),
(acc, current) => {
acc[current.FirstAndLastName] = current;
return acc;
});
其他回答
LINQ的解决方案:
// Use the first value in group
var _people = personList
.GroupBy(p => p.FirstandLastName, StringComparer.OrdinalIgnoreCase)
.ToDictionary(g => g.Key, g => g.First(), StringComparer.OrdinalIgnoreCase);
// Use the last value in group
var _people = personList
.GroupBy(p => p.FirstandLastName, StringComparer.OrdinalIgnoreCase)
.ToDictionary(g => g.Key, g => g.Last(), StringComparer.OrdinalIgnoreCase);
如果你更喜欢非linq解决方案，那么你可以这样做:
// Use the first value in list
var _people = new Dictionary<string, Person>(StringComparer.OrdinalIgnoreCase);
foreach (var p in personList)
{
if (!_people.ContainsKey(p.FirstandLastName))
_people[p.FirstandLastName] = p;
}
// Use the last value in list
var _people = new Dictionary<string, Person>(StringComparer.OrdinalIgnoreCase);
foreach (var p in personList)
{
_people[p.FirstandLastName] = p;
}
您可以创建一个类似于ToDictionary()的扩展方法，区别在于它允许重复。喜欢的东西:
public static Dictionary<TKey, TElement> SafeToDictionary<TSource, TKey, TElement>(
this IEnumerable<TSource> source,
Func<TSource, TKey> keySelector,
Func<TSource, TElement> elementSelector,
IEqualityComparer<TKey> comparer = null)
{
var dictionary = new Dictionary<TKey, TElement>(comparer);
if (source == null)
{
return dictionary;
}
foreach (TSource element in source)
{
dictionary[keySelector(element)] = elementSelector(element);
}
return dictionary;
}
在本例中，如果存在重复值，则最后一个值胜出。
大多数其他答案的问题是，他们使用Distinct, GroupBy或ToLookup，这在底层创建了一个额外的字典。同样ToUpper创建额外的字符串。 这就是我所做的，除了一处更改外，几乎完全复制了微软的代码:
public static Dictionary<TKey, TSource> ToDictionaryIgnoreDup<TSource, TKey>
(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer = null) =>
source.ToDictionaryIgnoreDup(keySelector, i => i, comparer);
public static Dictionary<TKey, TElement> ToDictionaryIgnoreDup<TSource, TKey, TElement>
(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer = null)
{
if (keySelector == null)
throw new ArgumentNullException(nameof(keySelector));
if (elementSelector == null)
throw new ArgumentNullException(nameof(elementSelector));
var d = new Dictionary<TKey, TElement>(comparer ?? EqualityComparer<TKey>.Default);
foreach (var element in source)
d[keySelector(element)] = elementSelector(element);
return d;
}
因为索引器上的set会导致它添加键，所以它不会抛出，也只会进行一次键查找。你也可以给它一个IEqualityComparer，例如StringComparer。OrdinalIgnoreCase
使用Distinct()和不分组的linq -解决方案是:
var _people = personList
.Select(item => new { Key = item.Key, FirstAndLastName = item.FirstAndLastName })
.Distinct()
.ToDictionary(item => item.Key, item => item.FirstFirstAndLastName, StringComparer.OrdinalIgnoreCase);
我不知道它是否比LukeH的解决方案更好，但它同样有效。
这应该适用于lambda表达式:
personList.Distinct().ToDictionary(i => i.FirstandLastName, i => i);
