CODEWITHSUNDEEP
c#linq
Adrian Rosca
Adrian Rosca

Reputation: 7412

How extract properties from several objects with LINQ

I often find myself doing the below to extract properties from a list of objects just to create an aggregated list. How would this be expressed with LINQ?

var totalErrors =
    new Dictionary<string, string>();

foreach (var res in results)
{
    foreach (var err in res.Errors)
    {
        totalErrors
            .Add(err.Key, err.Value);
    }
}

return totalErrors;

Upvotes: 0

Views: 162

Answers (3)

pascx64
pascx64

Reputation: 984

You can use SelectMany :

var allErrors = Results.SelectMany( res=>res.Errors );
//foreach( var error in allErrors )...

var dictionary = allErrors.ToDictionary( x=>x.Key, x=> x.Value );

Upvotes: 0

Farhad Jabiyev
Farhad Jabiyev

Reputation: 26635

You can use SelectMany and ToDictionary methods:

var result = results
     .SelectMany(x => x.Errors) // get all Errors in one sequence
     .ToDictionary(x => x.Key, x => x.Value); // create new dictionary based on this Enumerable

SelectMany() projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence. And ToDictionary() creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function.

Upvotes: 2

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726579

You can do an aggregation on two levels with SelectMany, like this:

var totalErrors = results
    .SelectMany(r => r.Errors)
    .ToDictionary(e => e.Key, e => e.Value);

SelectMany "flattens" a collection of collections into a single level, at which point you can apply ToDictionary to a flattened list.

Upvotes: 1

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