In C#, how do I check for duplicate elements inside of a list, then print the name of the duplicate element?

Question

I'm trying to sort a list alphabetically, then once the list is sorted, print the name of any element in the list which occurred more than once.

Most google searches only address comparing separate lists. I know you can compare strings, and that list elements (in this case are strings), but I'm not sure how to compare these strings since they're in the list.

using System;
using System.Collections.Generic;

namespace Challenge5alphabeticalOrderSorting
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            List<string> fruit = new List<string>()
            {
                "apple",
                "mango",
                "mango",
                "orange",
                "blueberry",
                "blueberry"
            };

            fruit.Sort();
            foreach (string f in fruit)
                Console.WriteLine(f);
        }
    }
}

You can use Linq, `GroupBy()` then `Select()` where `Count() > 1` — maccettura, Feb 04 '20 at 17:57
```fruit.GroupBy(name=>name, (k,g)=>new{ Name=k, Count=g.Count() }) .Where(g=>g.Count>1) .OrderByDescending(g=>g.Count) .Dump(); ``` see: http://share.linqpad.net/m8to6t.linq — mbx, Feb 04 '20 at 17:58
Does this answer your question? [C# LINQ find duplicates in List](https://stackoverflow.com/questions/18547354/c-sharp-linq-find-duplicates-in-list) — Christophe Chenel, Feb 04 '20 at 18:12

Pavel Anikhouski · Accepted Answer · 2020-03-12T12:29:28.610

3

The code below prints the duplicated names, as OP wants (not the count or something else), using GroupBy, Where and Count methods

print the name of any element in the list which occurred more than once.

var groups = fruit.GroupBy(f => f).Where(g => g.Count() > 1);
foreach (var group in groups)
    Console.WriteLine(group.Key);

edited Mar 12 '20 at 12:29

answered Feb 04 '20 at 19:00

Pavel Anikhouski

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In C#, how do I check for duplicate elements inside of a list, then print the name of the duplicate element?

1 Answers1