How to find duplicate values in List>?

Question

I have a List of Dictionary<string, object>. How to find duplicate values in all dictionaries by value?

Possible duplicate of [C#: Remove duplicate values from dictionary?](http://stackoverflow.com/questions/1462101/c-remove-duplicate-values-from-dictionary) — Tadija Bagarić, Mar 06 '17 at 06:49
posible duplicate of http://stackoverflow.com/questions/7172394/finding-duplicate-values-in-dictionary-and-print-key-of-the-duplicate-element — Axel Bouttelgier, Mar 06 '17 at 06:49
He's asking for finding duplicates in a `List` of `Dictionaries`. Those aren't exact duplicates. — Ilian, Mar 06 '17 at 06:52

Hamid Pourjam · Answer 1 · 2017-03-06T07:52:50.513

You can find duplicate values with their occurrences using LINQ. It gives you duplicate values and its occurrences (index in list and key in dictionary).

var duplicates = dicList
    .SelectMany((x, i) => x.Select(p => new { Index = i, Key = p.Key, Value = p.Value }))
    .GroupBy(x => x.Value)
    .Where(x => x.Count() > 1)
    .Select(x => new
        {
            Value = x.First().Value,
            Occurrences  = x.Select(o => new { Index = o.Index, Key = o.Key })
        });

If you just want duplicate values then use simplified version

var duplicates = listOfDic
    .SelectMany(x => x.Values)
    .GroupBy(x => x)
    .Where(x => x.Count() > 1);

Murad · Answer 2 · 2017-03-06T07:21:34.000

1

Use linq for compact code:

       List<Dictionary<string, object>> list = new List<Dictionary<string, object>>();
        list.SelectMany(dictionary => dictionary.Values).GroupBy(d => d).Where(x => x.Count() >1);

edited Mar 06 '17 at 07:21

answered Mar 06 '17 at 06:52

Murad

523
4
17

1

This works only with one dictionary. But not with a List. – Sebi Mar 06 '17 at 06:54

score 1 · Answer 3 · answered Mar 06 '17 at 06:59

Old classic loop

var uniqueValues = new HashSet<object>();
var duplicateValues = new List<object>();
foreach (var value in yourDictionaries.SelectMany(dict => dict.Values))
{
    if (uniqueValues.Add(value) == false)
    {
        duplicateValues.Add(value);
    }
}

SelectMany is a key method for getting all values of all dictionaries.

If you are fan of LINQ you can convert it to the LINQ expression for example by using Aggregate or GroupBy

How to find duplicate values in List>?

3 Answers3