c# - 从不同的字符串中获取前 6 个字符

Question

string[] arr = { "abcdefXXX872358", "abcdef200X8XXX58", "abcdef200X872359", "6T1XXXXXXXXXXXX11", "7AbcdeHA30XXX541", "7AbcdeHA30XXX691" };

我怎样才能从上面得到不同的数字，其中前 6 个字符必须是不同的结果将是

abcdefXXX872358

6T1XXXXXXXXXXXX11

7AbcdeHA30XXX541

我尝试这样的事情

var dist = (from c in arr
            select c).Select(a => a.Substring(0, 5)).Distinct();

这给了我前 5 个字符，但我想要整个字符串

Answer 1

对第一个字符进行分组，并获取每个组中的第一个字符串：

IEnumerable<string> firstInGroup =
   arr
   .GroupBy(s => s.Substring(0, 6))
   .Select(g => g.First());

Answer 2

我认为最好的方法是实现一个 IEqualityComparer，正如 List.Distinct() 的重载所暗示的那样

    public class firstXCharsComparer : IEqualityComparer<string>
    {
        private int numChars;
        public firstXCharsComparer(int numChars)
        {
            this.numChars = numChars;
        }

        public bool Equals(string x, string y)
        {
            return x.Substring(0, numChars) == y.Substring(0, numChars);
        }

        public int GetHashCode(string obj)
        {
            return obj.Substring(0, numChars).GetHashCode();
        }
    }
    static void Main(string[] args)
    {
        string[] arr = { "abcdefXXX872358", "abcdef200X8XXX58", "abcdef200X872359", "6T1XXXXXXXXXXXX11", "7AbcdeHA30XXX541", "7AbcdeHA30XXX691" };

        var result = arr.ToList().Distinct(new firstXCharsComparer(6));
        result.Count();
    }