Is there a better solution to this List sorting?

Question

I am writing a class for an ASP.NET MVC menu. I want to be able to take a list of all blog entries and make an Archive menu similar to this:

1/2011 (2)
3/2011 (1)
4/2011 (12)
etc...

Here is the code that I am using:

public class ArchiveMenuModel
{
    private List<ArchiveMenuItem> menuItems;
    public List<ArchiveMenuItem> MenuItems { get { return menuItems; } }

    public ArchiveMenuModel(List<DateTime> dates, string streamUrl)
    {
        menuItems = new List<ArchiveMenuItem>();
        int itemCount = 0;
        dates = dates.OrderByDescending(x => x).ToList();

        for (int i=0; i<dates.Count; i++)
        {
            itemCount++;
            if(i+1 < dates.Count)
            {
                if(!(dates[i].Month == dates[i + 1].Month && dates[i].Year == dates[i + 1].Year))
                {
                    menuItems.Add(new ArchiveMenuItem(streamUrl, dates[i].Month, dates[i].Year, itemCount));
                    itemCount = 0;
                }
            }
            else
            {
                menuItems.Add(new ArchiveMenuItem(streamUrl, dates[i].Month, dates[i].Year, itemCount));
            }
        }

    }
}

Is there a better way, perhaps by using Linq or something? Specifically, the part of my code that i don't like is:

if(!(dates[i].Month == dates[i + 1].Month && dates[i].Year == dates[i + 1].Year))

If I can avoid such an ugly if statement, that would be great!

Is there LINQ in there? ;-) See `OrderBy` and `GroupBy` found in [IEnumerable](http://msdn.microsoft.com/en-us/library/system.linq.enumerable.aspx). The latter will get your groups (can then count elements in each group), the former will get the groups ordered. Decorate with the "fancy LINQ syntax" ... or leave as normal method calls (my preferred way). This isn't an answer because I'm just not gonna plop down any code -- play around in [LINQPad](http://linqpad.net) for a bit and enjoy! — , Jul 01 '11 at 20:41
When I was trying that, I had trouble getting the entry count. Also, is `GroupBy` able of returning `DateTime` groups by month+year and not time? — quakkels, Jul 01 '11 at 20:45
Do you want to include empty months? I.e. lines like “5/2011 (0)”? — svick, Jul 01 '11 at 20:53
@svick - I was thinking that I wouldn't include empty months. Can't come up with a good reason to... at least not yet ;-) — quakkels, Jul 01 '11 at 21:00

Handcraftsman · Accepted Answer · 2011-07-01T21:15:51.227

2

menuItems = dates
     .GroupBy(x => new DateTime(x.Year, x.Month, 1))
     .Select(x=> new{Date = x.Key, Count = x.Count()})
     .OrderByDescending(x => x.Date)
     .Select(x => new ArchiveMenuItem(streamUrl, 
                                      x.Date.Month, 
                                      x.Date.Year, 
                                      x.Count))
     .ToList();

edited Jul 01 '11 at 21:15

answered Jul 01 '11 at 21:09

Handcraftsman

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score 1 · Answer 2 · answered Jul 01 '11 at 21:12

1

var menuItems = from date in dates
                group date by new { date.Year, date.Month } into g
                select new { g.Key.Year, g.Key.Month, Count = g.Count() } into month
                orderby month.Year, month.Month
                select new ArchiveMenuItem(streamUrl, month.Month, month.Year, month.Count);

This LINQ query

groups the dates by year and month
selects the year, month and number of dates for each group
orders the groups by year and month
creates ArchiveMenuItem for each group

answered Jul 01 '11 at 21:12

svick

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Thanks for the added explanation. It looks like you and Handrcraftsman are doing basically the same thing. – quakkels Jul 01 '11 at 21:19
@quakkels, yeah, it's basically the same. – svick Jul 01 '11 at 21:36

score 0 · Answer 3 · answered Jul 01 '11 at 21:07

var memuItems = dates.Select(o => o.Date.AddDays(-o.Date.Day + 1))
            .GroupBy(o => o, (o, p) => new {MonthAndYear = o.Date, EntriesCount = p.Count()})
            .Select(o => new ArchiveMenuItem(streamUrl, o.MonthAndYear.Month, o.MonthAndYear.Year, o.EntriesCount));

I subtract days to have date (to first of the month), so I can group using year and month.

score 0 · Answer 4 · answered Jul 01 '11 at 21:17

@svick and @danyolgiax,

Here's what I came up with from dany's link:

public class ArchiveMenuModel
{
    private List<ArchiveMenuItem> menuItems;
    public List<ArchiveMenuItem> MenuItems { get { return menuItems; } }

    public ArchiveMenuModel(List<DateTime> dates, string streamUrl)
    {
        menuItems = new List<ArchiveMenuItem>();
        dates = dates.OrderByDescending(x => x).ToList();

        var grouped = from d in dates
                        group d by new { month = d.Month, year= d.Year } into d     
                        select new { dt = d, count = d.Count() };
        foreach(var item in grouped)
        {
            menuItems.Add(new ArchiveMenuItem(streamUrl, item.dt.Key.month, item.dt.Key.year, item.count));
        }
    }
}

Sean Thoman · Answer 5 · 2011-07-01T21:12:09.070

-1

Something along these lines should work:

  menuItems.GroupBy(x => x.Month + "/" + x.Year);

I dont know the name of the property that holds the DateTime, but itd have to be set up like,

  menuItems.GroupBy(x => x.(datetime).Month + "/" + x.(datetime).Year);

edited Jul 01 '11 at 21:12

answered Jul 01 '11 at 20:56

Sean Thoman

7,429
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Why would you create a string to do that? – svick Jul 01 '11 at 21:03
The grouping works fine. Im not clear on what exactly is supposed to be in the list of DateTimes though. – Sean Thoman Jul 01 '11 at 21:13

Is there a better solution to this List sorting?

5 Answers5