How to get the range index of repeated elements. LINQ

Question

Thank

Dim MyArray as String()={"A","A","A","B","B","C","A","A"}

'Need Result as Array

0-2

3-4

5-5

6-7

Answer 1

If LINQ is required:

Dim MyArray As String() = {"A", "A", "A", "B", "B", "C", "A", "A"}

Dim result As String() = MyArray.
    Select(Function(v, i) New With {v, i}).
    GroupBy(Function(p) p.v).
    SelectMany(Function(g) g.Select(Function(p, i) New With {p.v, p.i, .d = p.i - i})).
    GroupBy(Function(z) New With {Key z.v, Key z.d}).
    Select(Function(g) New With {g.Key.v, .min = g.Min(Function(b) b.i), .max = g.Max(Function(b) b.i)}).
    OrderBy(Function(t) t.min).
    Select(Function(t) $"{t.min}-{t.max}").
    ToArray

The result is an array of strings like "0-2", "3-4", etc.

Answer 2

Hi there Mansour_Dalir

Thats a good question and thanks for using QandA platform.

try this code below

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static void Main()
    {
        string[] myArray = { "A", "A", "A", "B", "B", "C", "A", "A" };
        var result = GetRangeIndexes(myArray);
        foreach (var range in result)
        {
            Console.WriteLine($"{range.Item1}-{range.Item2}");
        }
    }
    static List<Tuple<int, int>> GetRangeIndexes(string[] array)
    {
        var result = new List<Tuple<int, int>>();
        int start = 0;
        int end = 0;
        for (int i = 1; i < array.Length; i++)
        {
            if (array[i] == array[i - 1])
            {
                end = i;
            }
            else
            {
                result.Add(new Tuple<int, int>(start, end));
                start = i;
                end = i;
            }
        }
    
        result.Add(new Tuple<int, int>(start, end));
        return result;
    }
}

If this helps kindly accept the answer thank much.