使用linq将列表转换为字典,而不必担心重复

Question

我有一个Person对象列表.我想转换为一个字典,其中键是名字和姓氏(连接),值是Person对象.

问题是我有一些重复的人,所以如果我使用这个代码会爆炸:

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,但我现在并不关心重复的名字.如果有多个名字我只想抓一个.无论如何,我可以在上面写这个代码,所以它只需要一个名字,并没有炸毁重复？

Answer 1

LINQ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);

如果您更喜欢非LINQ解决方案,那么您可以执行以下操作:

// 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;
}

Answer 2

这是明显的非linq解决方案:

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

Answer 3

使用Distinct()并且没有分组的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,但它也可以.

Answer 4

这应该适用于lambda表达式:

personList.Distinct().ToDictionary(i => i.FirstandLastName, i => i);

Answer 5

您还可以使用ToLookupLINQ函数,然后您可以将它与字典几乎互换使用.

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

这将基本上在LukeH的答案中进行GroupBy ,但是会给出Dictionary提供的散列.因此,您可能不需要将其转换为Dictionary,而只需First在需要访问键的值时使用LINQ 函数.

Answer 6

要处理消除重复项,请实现IEqualityComparer<Person>可在Distinct()方法中使用的方法,然后轻松获取字典.鉴于:

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; }
}

获取你的字典:

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);

Answer 7

您可以创建类似于ToDictionary()的扩展方法,区别在于它允许重复.就像是:

    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; 
    }

在这种情况下,如果有重复项,则最后一个值获胜.