How to delete an item from a Dictonary using LINQ in C#

Question

I need to delete a specific item from a dictonary..

The dictonary is like

      dict["Key1"]="Value1"
      dict["Key2"]="Value2"
      dict["Key3"]="Value3"
      dict["Key4"]="Value2"

How to delete the item if another item has the same value using LINQ

Thanks in advance

Which item do you want to delete, the item with Key2 or the one with Key4? — David_001, Jun 30 '10 at 06:41

score 3 · Answer 1 · edited May 23 '17 at 10:32

3

check orginal answer by @Jon Skeet : C#: Remove duplicate values from dictionary?

var uniqueValues = myDict.GroupBy(pair => pair.Value)
                         .Select(group => group.First())
                         .ToDictionary(pair => pair.Key, pair => pair.Value);

edited May 23 '17 at 10:32

Community

1
1

answered Jun 30 '10 at 06:33

Pranay Rana

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score 3 · Accepted Answer · answered Jun 30 '10 at 06:49

3

Here my tested solution:

dict.GroupBy(x => x.Value, x => x.Key)
.Where(x => x.Count() > 1)
.SelectMany(x => x.Skip(1))
.ToList().ForEach(x => dict.Remove(x))

answered Jun 30 '10 at 06:49

digEmAll

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This answer is actually clever. Didn't know about the GroupBy that takes a "select this" parameter. – Matt Mitchell Jun 30 '10 at 07:05

Matt Mitchell · Answer 3 · 2010-06-30T06:59:05.320

var dupKeys = dict.GroupBy(innerD => innerD.Value)
                .Where(mergedByValue => mergedByValue.Count() > 1)
                .Select(mergedByValue => mergedByValue.OrderByDescending(m => m.Key).First().Key);

dict.Where(d => dupKeys.Contains(d.Key)).ToList()
  .ForEach(d => dict.Remove(d.Key));

This assumes you want the last duplicate removed, where last is defined as the last ordinal string value.

If you want all duplicates removed, change your dupKeys to this:

var dupKeys = dict.GroupBy(innerD => innerD.Value)
                .Where(mergedByValue => mergedByValue.Count() > 1).Dump()
                .SelectMany(mergedByValue => mergedByValue.Select(m => m.Key));

score 0 · Answer 4 · answered Jun 30 '10 at 06:31

0

You need to use Distinct.

answered Jun 30 '10 at 06:31

Incognito

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@ Incognito: Thank you... you are correct but i need to remove the duplicates after creating the dictonary. – Thorin Oakenshield Jun 30 '10 at 06:33
& Pramodh, You are not correct, distinct will not help you filter a collection based on a property of the objects and still use associated properties. – Matt Mitchell Jun 30 '10 at 06:47
Have you checked the link. This is not SQL distinct. You can use it on existing dictionary. – Incognito Jun 30 '10 at 06:47
yes? now try and use it to get the keys of all distinct values. – Matt Mitchell Jun 30 '10 at 06:48
@Graphain I agree it gives you way to get distinct values easily. – Incognito Jun 30 '10 at 07:14

How to delete an item from a Dictonary using LINQ in C#

4 Answers4