How to avoid duplicates in LINQ for an anonymous type?

Question

I am trying to convert a DataTable to a Dictionary of string and integer. DataTable has duplicates and I had written the following code:

Dictionary<string, short> data = dt.AsEnumerable()
                                   .Select(item => new {
                                                          Key = item.Field<string>("product_name"),
                                                          Value = item.Field<short>("type_id")
                                                        })
                                    .Distinct()
                                    .ToDictionary(dr => dr.Key, dr => dr.Value, StringComparer.OrdinalIgnoreCase);

When I have data like this:

Product1   1
Product1   2
Product2   3
Product4   3

the result should be this:

Product1   1
Product2   3
Product4   3

My code is erroring out as the Distinct() considers all the available properties in the anonymous type. Is there a way to achieve this linq or overwrite the default behavior of Distinct()?

How many properties are involved in determining if it's distinct? Is it just the key? — Dave, Feb 24 '16 at 22:25
Yes, Just the key. I need get all the distinct product_name with the corresponding type_id (this can be first the first occurrence of the key). — PushCode, Feb 24 '16 at 22:27

score 4 · Accepted Answer · answered Feb 24 '16 at 22:27

Try this (distinct by Key):

Dictionary<string, short> data = dt.AsEnumerable()
                                       .Select(item => new {
                                                              Key = item.Field<string>("product_name"),
                                                              Value = item.Field<short>("type_id")
                                                            })
                                        .GroupBy(x=>x.Key)
                                        .Select(x=>x.First())
                                        .ToDictionary(dr => dr.Key, dr => dr.Value, StringComparer.OrdinalIgnoreCase);

Yep. That's what I was going to suggest, too. – Dave Feb 24 '16 at 22:28 — Dave, Feb 24 '16 at 22:28

score 1 · Answer 2 · edited May 23 '17 at 12:31

1

You can provide an implementation of IEqualityComparer to Distinct() as per the docs: https://msdn.microsoft.com/library/bb338049(v=vs.100).aspx

You can create such an equality comparer for your anonymous type as described in this stack overflow answer: https://stackoverflow.com/a/1071637/1675729

edited May 23 '17 at 12:31

Community

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answered Feb 24 '16 at 22:25

NWard

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How to avoid duplicates in LINQ for an anonymous type?

2 Answers2