using System;
using System.Globalization;
using System.Linq;
using System.Collections.Generic;
 
public class Test
{
 
 
	public static void Main()
	{
        string[] array1 = new[] { "100101","100102" ,"100101","100104","100101"    };
        string[] array2 = new[] {  "Testing123", "Apple123", "Dog123","Cat123", "Animal123" };
 
        var strings = array1.Select((s,index) => new{ s, index })
	    .GroupBy(x => x.s)
	    .Select(g => 
	        string.Join(" ", g.Select(x => array2.ElementAtOrDefault(x.index)).ToArray()));
 
		foreach(string s in strings)
		    Console.WriteLine(s);
	}
}

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