Question

Is there a way that I could return duplicate values from an array in C#? also im looking to write a small algorithm that would return the most number of duplicate values in an array. for example

[1, 2,2,2 3,3] I need to return the duplicate values with the most number of occurrences and the number of occurrences as well.

I think I saw some post which said that It could be done using Linq but I have no clue what Linq is

Any help would be much appreciated.

Answer 1

Try this:

int[] data = new int[] { 1, 2, 2, 2, 3, 3 };
IGrouping<int, int> mostOccurrences = data
    .GroupBy(value => value)
    .OrderByDescending(group => group.Count())
    .First();

Console.WriteLine("Value {0} occurred {1} time(s).", mostOccurrences.Key, mostOccurrences.Count());

Note that if multiple values occur the same number of times (such as if you added another 3 to that list), the above code will only list one of them. To handle that situation, try this:

int[] data = new int[] { 1, 2, 2, 2, 3, 3, 3 };
var occurrenceInfos = data
    .GroupBy(value => value)
    .Select(group =>
        new {
            Count = group.Count(),
            Value = group.Key
        }
    );
int maxOccurrenceCount = occurrenceInfos.Max(info => info.Count);
IEnumerable<int> maxOccurrenceValues = occurrenceInfos
    .Where(info => info.Count == maxOccurrenceCount)
    .Select(info => info.Value);

foreach (int value in maxOccurrenceValues)
    Console.WriteLine("Value {0} occurred {1} time(s).", value, maxOccurrenceCount);