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copied!<p>The main understanding is to use the IEqualityComparer, the class LambdaCustomComparer is a helper to do that using LINQ dynamically. </p> <p>You need copy and Paste this :</p> <hr> <pre><code>public class User { public string Name { get; set; } public string Sex { get; set; } public DateTime Birthday { get; set; } public int? FilterId { get; set; } } public class LambdaCustomComparer<T> : IEqualityComparer<T> { private readonly Func<T, T, bool> lambdaComparer; private readonly Func<T, int> lambdaHash; public LambdaCustomComparer(Func<T, T, bool> lambdaComparer, bool ignoreHashcode = true) { if (lambdaComparer == null) throw new ArgumentNullException("lambdaComparer"); this.lambdaComparer = lambdaComparer; if (ignoreHashcode) lambdaHash = obj => 0; else lambdaHash = EqualityComparer<T>.Default.GetHashCode; } public LambdaCustomComparer(Func<T, T, bool> lambdaComparer, Func<T, int> lambdaHash) { if (lambdaComparer == null) throw new ArgumentNullException("lambdaComparer"); if (lambdaHash == null) throw new ArgumentNullException("lambdaHash"); this.lambdaComparer = lambdaComparer; this.lambdaHash = lambdaHash; } public bool Equals(T x, T y) { return lambdaComparer(x, y); } public int GetHashCode(T obj) { return lambdaHash(obj); } } var list = new List<User> { new User() {Name = "Josh", Sex= "M", Birthday = DateTime.Now, FilterId = null}, new User() {Name = "John", Sex= "M", Birthday = DateTime.Now, FilterId = null}, new User() {Name = "Jane", Sex= "F", Birthday = DateTime.Now, FilterId = null}, new User() {Name = "Josh", Sex= "M", Birthday = DateTime.Now, FilterId = 1}, new User() {Name = "John", Sex= "M", Birthday = DateTime.Now, FilterId = null}, }; var comparer = new LambdaCustomComparer<User>((a, b) => a.Name == b.Name && a.Birthday.Date == b.Birthday.Date && a.Sex == b.Sex && a.FilterId == b.FilterId); var distinctList = list.GroupBy(user => user, comparer).ToDictionary(a => a.Key, b => b.ToArray()); </code></pre>

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