Linq Grouping by Date (month)

Question

I would like to know how I could group some data by month and sum a field. For example I have a list of MyObjects(DateTimeField, AmountField). I want to group by DateTimeField, but not entire date, just by month, and then sum the AmountField for each month.

I don't know why the objectgrouped is null?

    IEnumerable<MyObject> objectList= GetMyObject();

    var ObjectGrouped = objectList.GroupBy(l => l.ObjectDate.GetValueOrDefault().Month)
                          .Select(lg =>
                                new
                                {
                                    CurrentMonth = lg.Key,
                                    Total = lg.Sum(w => w.ObjectAmount)
                                });

ObjectDate      ObjectAmount

1/1/2013              3.3
3/1/2013              6.9
13/2/2013            5
3/4/2013              3.6
13/4/2013            15.2

Very similar: http://stackoverflow.com/questions/11574474/linq-get-sum-of-data-group-by-date — George Johnston, Apr 12 '13 at 19:33

D Stanley · Answer 1 · 2013-04-12T20:00:10.927

6

~~I assume by "month" you mean "month and year":~~

To ignore null values:

var query = myList.Where(i => i.DateTimeField.HasValue)
                  .GroupBy(i => i.DateTimeField.Value.Month)
                  .Select(g => new {
                            Month=g.Key,
                            Total=g.Sum(i=>i.AmountField) 
                         });

to put null values in a separate bucket ("0" month):

var query = myList.GroupBy(i => i.DateTimeField.HasValue ? i.DateTimeField.Value.Month : 0)
                  .Select(g => new {
                            Month=g.Key,
                            Total=g.Sum(i=>i.AmountField) 
                         });

edited Apr 12 '13 at 20:00

answered Apr 12 '13 at 19:48

D Stanley

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No, just the month, because before I get all the data from the current year. But I cant do DateTime.Month, I think is because it is a Nullable, what could I do? Thanks – user2112420 Apr 12 '13 at 19:56
How do you want to handle null values? Do they go in their own bucket or are they ignored? – D Stanley Apr 12 '13 at 19:57
It is just a Model and DataBase thing, but it is always not null on the DB. – user2112420 Apr 12 '13 at 19:59

score 2 · Answer 2 · answered Apr 12 '13 at 19:34

2

Try this:

List<DateTime> list = new List<DateTime>();
var grouppedResult = list.GroupBy(x => x.Month);

answered Apr 12 '13 at 19:34

Nikolay Kostov

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I have not a field Month, I just have a field type DateTime, but I only want to group by Month and then sum all the amount of each month. – user2112420 Apr 12 '13 at 19:41
class MyModel { public DateTime Time { get; set; } } List list... list.GroupBy(x => x.Time.Month); – Nikolay Kostov Apr 12 '13 at 19:43
I dont know why I cant do that, by the way the DateTime is a Nullable, is because of that? – user2112420 Apr 12 '13 at 19:54
@user2112420 did you try `GetValueOrDefault().Month` – Conrad Frix Apr 12 '13 at 19:58

score 1 · Answer 3 · answered Apr 12 '13 at 19:44

1

var groups = list.GroupBy(l => l.DateTimeField.Year * 12 + l.DateTimeField.Month)
                .Select(g => new {
                                Month=g.First().DateTimeField,
                                Sum=g.Select(a=>a.AmountField).Sum() 
                             })
                .ToList();

answered Apr 12 '13 at 19:44

I4V

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I dont know why I am not getting nothing on the group this is null, and my list has values... – user2112420 Apr 12 '13 at 20:13

Linq Grouping by Date (month)

3 Answers3