从具有常见值的字典中获取 TKey，其中 TValue 为 List<string>

Question

我有一本看起来像这样的字典：Dictionary<string, List<string>> dict = new Dictionary<string, List<string>>(){    {"a" , new List<string> { "Red","Yellow"} },    {"b" , new List<string> { "Blue","Red"} },    {"c" , new List<string> { "Green","Orange"} },    {"d" , new List<string> { "Black","Green"} },};我需要作为字典输出，dict其中的公共值List<string>应该是键，值应该是键列表。例如：Red: [a,b]Green: [c,d]我不知道如何用listin dictionaryas解决这个问题TValue。请解释我如何处理字典中的列表。

Answer 1

您可以用扁平化您的字典SelectMany并获得看起来像的简单列表

"a" - "Red"

"a" - "Yellow"

"b" - "Blue"

"b" = "Red"

// and so on

然后按值分组并从这些组中构建一个新字典。试试这个代码：

var commonValues = dict.SelectMany(kv => kv.Value.Select(v => new {key = kv.Key, value = v}))

    .GroupBy(x => x.value)

    .Where(g => g.Count() > 1)

    .ToDictionary(g => g.Key, g => g.Select(x => x.key).ToList());

Answer 2

很多循环......循环遍历字典，然后循环遍历列表中的每个值。

var result = new Dictionary<string, List<string>>();

// Loop through each key/value pair in the dictionary

foreach (var kvp in dict)

{

    // kvp.Key is the key ("a", "b", etc)

    // kvp.Value is the list of values ("Red", "Yellow", etc)

    // Loop through each of the values

    foreach (var value in kvp.Value)

    {

        // See if our results dictionary already has an entry for this

        // value. If so, grab the corresponding list of keys. If not,

        // create a new list of keys and insert it.

        if (!result.TryGetValue(value, out var list))

        {

            list = new List<string>();

            result.Add(value, list);

        }

        // Add our key to this list of keys

        list.Add(kvp.Key);

    }

}

如果您想通过包含多个项目的条目来过滤它，那么您可以执行以下操作：

result = result.Where(x => x.Value.Count > 1).ToDictionary(x => x.Key, x => x.Value);

或者，您可以避免循环并改用 Linq：

// Flatten the dictionary into a set of tuples

// e.g. (a, Red), (a, Yellow), (b, Blue), (b, Red), etc

var result = dict.SelectMany(kvp => kvp.Value.Select(color => (key: kvp.Key, color)))

    // Group by the value, taking the color as the elements of the group

    // e.g. (Red, (a, b)), (Yellow, (a)), etc

    .GroupBy(item => item.color, item => item.key)

    // Filter to the ones with more than one item

    .Where(group => group.Count() > 1)

    // Turn it into a dictionary, taking the key of the grouping

    // (Red, Green, etc), as the dictionary key

    .ToDictionary(group => group.Key, group => group.ToList());

您还可以使用 linq 查询语法，该语法稍长，但避免了SelectMany:

var result =

    (

        from kvp in dict

        from color in kvp.Value

        group kvp.Key by color into grp

        where grp.Count() > 1

        select grp

    ).ToDictionary(grp => grp.Key, grp => grp.ToList());