我有一本看起來像這樣的字典：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"} },};我需要作為字典輸出，dict其中的公共值List<string>應該是鍵，值應該是鍵列表。例如：Red: [a,b]Green: [c,d]我不知道如何用listin dictionaryas解決這個問題TValue。請解釋我如何處理字典中的列表。
2 回答
楊__羊羊
TA貢獻1943條經驗 獲得超7個贊
您可以用扁平化您的字典SelectMany并獲得看起來像的簡單列表
"a" - "Red"
"a" - "Yellow"
"b" - "Blue"
"b" = "Red"
// and so on
然后按值分組并從這些組中構建一個新字典。試試這個代碼：
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());
墨色風雨
TA貢獻1853條經驗 獲得超6個贊
很多循環......循環遍歷字典，然后循環遍歷列表中的每個值。
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);
}
}
如果您想通過包含多個項目的條目來過濾它，那么您可以執行以下操作：
result = result.Where(x => x.Value.Count > 1).ToDictionary(x => x.Key, x => x.Value);
或者，您可以避免循環并改用 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());
您還可以使用 linq 查詢語法，該語法稍長，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());
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