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C# 練習 - 在陣列中找出連續重複出現項目

 1 year ago
source link: https://blog.darkthread.net/blog/find-repeated-item-group/
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C# 練習 - 在陣列中找出連續重複出現項目

calendar.svg 2022-12-06 10:03 PM comment.svg 1 eye.svg 2,311

專案出現的小需求：想在陣列挑出連續重複出現的項目，例如要從陣列 [A, B, B, C, X, C, C, B, B, D, D, D] 挑出 [B, B]、[C, C]、[B, B]、[D, D, D] 四個群組。

這題目的難易度用來暖身剛好，適合用 yield return 來解。

最後琢磨成品如下：

IEnumerable<IEnumerable<T>> FindRepeatItemGroups<T>(IEnumerable<T> list, Func<T, T, bool> areEqual)
{
    if (list.Any())
    {
        var grp = new List<T>() { list.First() };
        foreach (var item in list.Skip(1))
        {
            if (areEqual(grp.Last(), item))
            {
                grp.Add(item);
            }
            else
            {
                if (grp.Count() > 1)
                    yield return grp;
                grp = new List<T>() { item };
            }
        }
        if (grp.Count() > 1)
            yield return grp;
    }
}

函式接收 IEnumerable<T> 作為搜尋對象，是否重複出現由 Func<T, T, bool> 決定，呼叫時傳入 (a, b) => a.SomeProp == b.SomeProp 自訂比對條件。函式使用 List<T> 蒐集重複出現的物件，以 foreach 巡覽所有元素，遇到目前物件與 List<T> 保存物件不相等時，檢查 List<T> 個數若大於一，表示連續出現，yield return 傳回 List<T> 清空 List<T> 重新統計。

測試範例如下：

var raw = "A,B,B,C,X,C,C,B,B,D,D,D".Split(',');
var i = 1;
var items = raw.Select(o => new
{
    Id = i++,
    Code = o
}).ToArray();
Console.ForegroundColor = ConsoleColor.White;
Console.WriteLine("Source: ");
foreach (var item in items)
{
    Console.ForegroundColor = ConsoleColor.DarkGray;
    Console.Write($"{item.Id}.");
    Console.ForegroundColor = ConsoleColor.Yellow;
    Console.Write($"{item.Code} ");
}
Console.WriteLine();
Console.ForegroundColor = ConsoleColor.Cyan;
var grps = FindRepeatItemGroups(items, (a, b) => a.Code == b.Code);
foreach (var grp in grps)
{
    Console.Write($"Group of {grp.First().Code} :");
    Console.WriteLine($" {string.Join(", ", grp.Select(o => o.Id))}");
}
Console.ResetColor();

IEnumerable<IEnumerable<T>> FindRepeatItemGroups<T>(IEnumerable<T> list, 
        Func<T, T, bool> areEqual)
{
    if (list.Any())
    {
        var grp = new List<T>() { list.First() };
        foreach (var item in list.Skip(1))
        {
            if (areEqual(grp.Last(), item))
            {
                grp.Add(item);
            }
            else
            {
                if (grp.Count() > 1)
                    yield return grp;
                grp = new List<T>() { item };
            }
        }
        if (grp.Count() > 1)
            yield return grp;
    }
}

Fig1_638059323956943574.png

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