在列表 C# 中搜索特定的重复键

Question

我有一个名为 "listA" 的列表，其中包含 1 个名为 "fieldA" 的字段，数据为

{1,0,0,0,1}

我只想检测“1”是否重复，如果“0”重复则不算重复

我试试

 var dupl = listA
                            .GroupBy(i => i.fieldA=="1")
                            .Where(g => g.Count() > 1)
                            .Select(g => g.Key).ToList();
 if (dupl.Count()>0){"you have duplicated 1"}

但“0”仍被检测为重复，我的 linq 有什么问题？

Answer 1

如果你只想知道是否有重复的 1 那么只需使用 Count:

bool isDuplicate = listA.Count(x => x.fieldA == "1") > 1;

Answer 2

你可以试试这个：

bool oneIsDuplicate = listA.Where(x=>x.fieldA=="1").Count() > 1;

Answer 3

这篇文章可能会有帮助。这里我们避免了在到达集合结束之前满足条件时的额外迭代。（我们不迭代整个集合以防在集合结束之前满足条件因此它有点多明智地调整性能）。

public static class Extentions
    {
        /// <summary>
        /// Used to find if an local variable aggreation based condition is met in a collection of items.
        /// </summary>
        /// <typeparam name="TItem">Collection items' type.</typeparam>
        /// <typeparam name="TLocal">Local variable's type.</typeparam>
        /// <param name="source">Inspected collection of items.</param>
        /// <param name="initializeLocalVar">Returns local variale initial value.</param>
        /// <param name="changeSeed">Returns desired local variable after each iteration.</param>
        /// <param name="stopCondition">Prediate to stop the method execution if collection hasn't reached last item.</param>
        /// <returns>Was stop condition reached before last item in collection was reached.</returns>
        /// <example> 
        ///  var numbers = new []{1,2,3};
        ///  bool isConditionMet = numbers.CheckForLocalVarAggreatedCondition(
        ///                                             () => 0, // init
        ///                                             (a, i) => i == 1 ? ++a : a, // change local var if condition is met 
        ///                                             (a) => a > 1);   
        /// </example>
        public static bool CheckForLocalVarAggreatedCondition<TItem, TLocal>(
                                this IEnumerable<TItem> source,
                                Func<TLocal> initializeLocalVar,
                                Func<TLocal, TItem, TLocal> changeSeed,
                                Func<TLocal, bool> stopCondition)
        {
            TLocal local = default(TLocal);
            foreach (TItem item in source)
            {
                local = changeSeed(local, item);
                if (stopCondition(local))
                {
                    return true;
                }
            }

            return false;
        }
    }

在列表 C# 中搜索特定的重复键

Search Specific Duplicated keys in List C#

c#

linq

list