如何檢查字典是否包含列表中的項目

Question

如何檢查字典是否包含列表中的項目。 我有以下字典和以下列表：

public static List<string> DixieStatesList = new List<string>
        {
            "Alabama", "Arkansas", "Floryda", "Georgia", "KarolinaPołudniowa", "KarolinaPółnocna",
            "Kentucky", "Luizjana", "Mississippi", "Missouri", "Oklahoma", "Teksas", "Tennesee", "Wirginia",
            "WirginiaZachodnia"
        };

public static Dictionary<string, float> WallaceNPPFRpopularities = new Dictionary<string, float>()
        {
            {"Alabama", 6}, {"Alaska", 2}, {"Arizona", 1}, {"Arkansas", 4}, {"Connecticut", 2},
            {"DakotaPołudniowa", 5}, {"DakotaPółnocna", 5}, {"Delaware", 4}, {"Floryda", 4},
            {"Georgia",  6}, {"Idaho", 1.5f}, {"Illinois", 2}, {"Indiana", 5}, {"Iowa", 2},
            {"Kalifornia", 4}, {"Kansas", 5}, {"KarolinaPołudniowa", 6}, {"KarolinaPółnocna", 5},
            {"Kentucky", 3}, {"Kolorado", 3}, {"Luizjana", 4}, {"Maine", 6}, {"Maryland", 5},
            {"Massachusets", 2 }, {"Michigan", 5}, {"Minnesota", 1.5f}, {"Mississippi", 6},
            {"Missouri", 2}, {"Montana", 1.5f}, {"Nebraska", 2}, {"Nevada", 4}, {"NewHampshire", 2},
            {"NewJersey", 4}, {"NowyJork", 1.5f}, {"NowyMeksyk", 2}, {"Ohio", 4}, {"Oklahoma", 4},
            {"Oregon", 1}, {"Pensylwania", 1.5f}, {"RhodeIsland", 3}, {"Teksas", 4}, {"Tennesee", 4},
            {"Utah", 1.5f}, {"Vermont", 5}, {"Waszyngton", 1}, {"Wirginia", 6}, {"WirginiaZachodnia", 6},
            {"Wisconsin", 1.5f}, {"Wyoming", 2}
        };

我想使用'foreach'或'if'或兩者來檢查這個字典是否包含列表中的一個元素並最終改變字典中元素的值，它與列表中的元素具有相同的鍵0.25 F。

Answer 1

我在 c# 之前從未接觸過，但你想要那樣的東西。 而且我不認為您可以更改靜態字典，但是，如果它不是靜態的，這是一種方法：

foreach(string key in DixieStatesList){

if(WallaceNPPFRpopularities.ContainsKey(key)
    WallaceNPPFRpopularities[key] =+ 0.25;

}

Answer 2

您可以使用Enumerable.Intersect 方法：

const float Increment = .25f;
foreach (string state in WallaceNPPFRpopularities.Keys.Intersect(DixieStatesList))
{
    WallaceNPPFRpopularities[state] += Increment;

    // Incremented "Alabama" popularity to 6.25.
    // Incremented "Arkansas" popularity to 4.25.
    // Incremented "Floryda" popularity to 4.25.
    // Incremented "Georgia" popularity to 6.25.
    // Incremented "KarolinaPołudniowa" popularity to 6.25.
    // Incremented "KarolinaPółnocna" popularity to 5.25.
    // Incremented "Kentucky" popularity to 3.25.
    // Incremented "Luizjana" popularity to 4.25.
    // Incremented "Mississippi" popularity to 6.25.
    // Incremented "Missouri" popularity to 2.25.
    // Incremented "Oklahoma" popularity to 4.25.
    // Incremented "Teksas" popularity to 4.25.
    // Incremented "Tennesee" popularity to 4.25.
    // Incremented "Wirginia" popularity to 6.25.
    // Incremented "WirginiaZachodnia" popularity to 6.25.
    Console.WriteLine(@$"Incremented ""{state}"" popularity to {WallaceNPPFRpopularities[state]}.");
}

Answer 3

您可以簡單地使用 Dictionary 上的 ContainsKey 來測試鍵是否存在，如果存在則使用索引獲取結果。

        float result = -1;

        if(WallaceNPPFRpopularities.ContainsKey("Alaska"))
        {
            result = WallaceNPPFRpopularities["Alaska"];
        }

Answer 4

嘗試這個

    foreach (var key in DixieStatesList)
    {
        if (WallaceNPPFRpopularities.ContainsKey(key))
            WallaceNPPFRpopularities[key] += 0.25f;
    }