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c#linqgroup-by
Jeff
Jeff

Reputation: 785

Linq select to new object

I have a linq query 

var x = (from t in types select t).GroupBy(g =>g.Type)

which groups objects by their type, as a result I want to have single new object containing all of the grouped objects and their count. Something like this:

type1, 30    
type2, 43    
type3, 72

to be more clear: grouping results should be in one object not an object per item type

Upvotes: 55

Views: 321374

Answers (6)

Pranay Rana
Pranay Rana

Reputation: 176886

Read : 101 LINQ Samples in that LINQ - Grouping Operators from Microsoft MSDN site

var x = from t in types  group t by t.Type
         into grp    
         select new { type = grp.key, count = grp.Count() };

For a single object, make use of StringBuilder and append it, or convert this in the form of dictionary:

    // fordictionary 
  var x = (from t in types  group t by t.Type
     into grp    
     select new { type = grp.key, count = grp.Count() })
   .ToDictionary( t => t.type, t => t.count); 

   //for stringbuilder not sure for this 
  var x = from t in types  group t by t.Type
         into grp    
         select new { type = grp.key, count = grp.Count() };
  StringBuilder MyStringBuilder = new StringBuilder();

  foreach (var res in x)
  {
       //: is separator between to object
       MyStringBuilder.Append(result.Type +" , "+ result.Count + " : ");
  }
  Console.WriteLine(MyStringBuilder.ToString());

Upvotes: 50

Garnet R. Chaney
Garnet R. Chaney

Reputation: 81

This is a great article for syntax needed to create new objects from a LINQ query.

But, if the assignments to fill in the fields of the object are anything more than simple assignments, for example, parsing strings to integers, and one of them fails, it is not possible to debug this. You can not create a breakpoint on any of the individual assignments.

And if you move all the assignments to a subroutine, and return a new object from there, and attempt to set a breakpoint in that routine, you can set a breakpoint in that routine, but the breakpoint will never be triggered.

So instead of:

var query2 = from c in doc.Descendants("SuggestionItem")
                select new SuggestionItem
                       { Phrase = c.Element("Phrase").Value
                         Blocked = bool.Parse(c.Element("Blocked").Value),
                         SeenCount = int.Parse(c.Element("SeenCount").Value)
                       };

Or

var query2 = from c in doc.Descendants("SuggestionItem")
                         select new SuggestionItem(c);

I instead did this:

List<SuggestionItem> retList = new List<SuggestionItem>();

var query = from c in doc.Descendants("SuggestionItem") select c;

foreach (XElement item in query)
{
    SuggestionItem anItem = new SuggestionItem(item);
    retList.Add(anItem);
}

This allowed me to easily debug and figure out which assignment was failing. In this case, the XElement was missing a field I was parsing for to set in the SuggestionItem.

I ran into these gotchas with Visual Studio 2017 while writing unit tests for a new library routine.

Upvotes: 1

dckuehn
dckuehn

Reputation: 2475

The answers here got me close, but in 2016, I was able to write the following LINQ:

List<ObjectType> objectList = similarTypeList.Select(o =>
    new ObjectType
    {
        PropertyOne = o.PropertyOne,
        PropertyTwo = o.PropertyTwo,
        PropertyThree = o.PropertyThree
    }).ToList();

Upvotes: 67

Jon Skeet
Jon Skeet

Reputation: 1499760

All of the grouped objects, or all of the types? It sounds like you may just want:

var query = types.GroupBy(t => t.Type)
                 .Select(g => new { Type = g.Key, Count = g.Count() });

foreach (var result in query)
{
    Console.WriteLine("{0}, {1}", result.Type, result.Count);
}

EDIT: If you want it in a dictionary, you can just use:

var query = types.GroupBy(t => t.Type)
                 .ToDictionary(g => g.Key, g => g.Count());

There's no need to select into pairs and then build the dictionary.

Upvotes: 41

daryal
daryal

Reputation: 14919

var x = from t in types
        group t by t.Type into grouped
        select new { type = grouped.Key,
                     count = grouped.Count() };

Upvotes: 4

Steve
Steve

Reputation: 2345

If you want to be able to perform a lookup on each type to get its frequency then you will need to transform the enumeration into a dictionary.

var types = new[] {typeof(string), typeof(string), typeof(int)};
var x = types
        .GroupBy(type => type)
        .ToDictionary(g => g.Key, g => g.Count());
foreach (var kvp in x) {
    Console.WriteLine("Type {0}, Count {1}", kvp.Key, kvp.Value);
}
Console.WriteLine("string has a count of {0}", x[typeof(string)]);

Upvotes: 1

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