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;
}

下面是一个明显的非linq解决方案:

foreach(var person in personList)
{
  if(!myDictionary.ContainsKey(person.FirstAndLastName))
    myDictionary.Add(person.FirstAndLastName, person);
}

如果你不介意总是添加最后一个，你可以避免这样的双重查找:

foreach(var person in personList)
{
    myDictionary[person.FirstAndLastName] = person;
}

要处理消除重复，实现一个IEqualityComparer<Person>，可以在Distinct()方法中使用，然后获取字典就很容易了。 考虑到:

class PersonComparer : IEqualityComparer<Person>
{
    public bool Equals(Person x, Person y)
    {
        return x.FirstAndLastName.Equals(y.FirstAndLastName, StringComparison.OrdinalIgnoreCase);
    }

    public int GetHashCode(Person obj)
    {
        return obj.FirstAndLastName.ToUpper().GetHashCode();
    }
}

class Person
{
    public string FirstAndLastName { get; set; }
}

拿出你的字典:

List<Person> people = new List<Person>()
{
    new Person() { FirstAndLastName = "Bob Sanders" },
    new Person() { FirstAndLastName = "Bob Sanders" },
    new Person() { FirstAndLastName = "Jane Thomas" }
};

Dictionary<string, Person> dictionary =
    people.Distinct(new PersonComparer()).ToDictionary(p => p.FirstAndLastName, p => p);

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);

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。

您还可以使用ToLookup LINQ函数，然后您几乎可以与Dictionary互换使用该函数。

_people = personList
    .ToLookup(e => e.FirstandLastName, StringComparer.OrdinalIgnoreCase);
_people.ToDictionary(kl => kl.Key, kl => kl.First()); // Potentially unnecessary

这将在LukeH的回答中执行GroupBy，但将给出Dictionary提供的散列。因此，您可能不需要将它转换为Dictionary，但只要在需要访问键的值时使用LINQ First函数即可。

从Carra的解开始，你也可以把它写成:

foreach(var person in personList.Where(el => !myDictionary.ContainsKey(el.FirstAndLastName)))
{
    myDictionary.Add(person.FirstAndLastName, person);
}

        DataTable DT = new DataTable();
        DT.Columns.Add("first", typeof(string));
        DT.Columns.Add("second", typeof(string));

        DT.Rows.Add("ss", "test1");
        DT.Rows.Add("sss", "test2");
        DT.Rows.Add("sys", "test3");
        DT.Rows.Add("ss", "test4");
        DT.Rows.Add("ss", "test5");
        DT.Rows.Add("sts", "test6");

        var dr = DT.AsEnumerable().GroupBy(S => S.Field<string>("first")).Select(S => S.First()).
            Select(S => new KeyValuePair<string, string>(S.Field<string>("first"), S.Field<string>("second"))).
           ToDictionary(S => S.Key, T => T.Value);

        foreach (var item in dr)
        {
            Console.WriteLine(item.Key + "-" + item.Value);
        }

如果我们想要返回字典中的所有Person(而不是只有一个Person)，我们可以:

var _people = personList
.GroupBy(p => p.FirstandLastName)
.ToDictionary(g => g.Key, g => g.Select(x=>x));

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LINQ等效的foldLeft功能

persons.Aggregate(new Dictionary<string,Person>(StringComparer.OrdinalIgnoreCase),
  (acc, current) => { 
    acc[current.FirstAndLastName] = current; 
    return acc; 
  });