Group By Dates using Linq

Question

What I have is a set of users with join dates and I want to use GoogleChartSharp to create a chart showing how many users have joined each month.

So I have this set of dates (US format) in a list:

01/01/2009

02/01/2009

02/12/2009

03/02/2009

03/12/2009

03/22/2009

Googlechartsharp requires me to do something like this:

string[] monthYears  = new string[] { "01/2009", "02/2009", "03/2009"};
int[] number= new int[] {1,2,3};

LineChart chart = new LineChart(150, 150);
chart.SetData(data);
chart.SetLegend(monthYears);

string url = chart.GetUrl();

How do I utilize linq to get the list of dates into arrays required by google? Or is Linq even the right tool?

Answer 1

Asusming those numvers are the number of times each month occurs. Then you could do something like this:

var numbers = from d in monthYears .Select(x => DateTime.Parse(x))
group d by d.Month into dg
select dg.Count();

That will give you an IEnumerable of the count for each. If you need it as an array it is not too hard to convert that to an array.

Answer 2

Sure, Linq is an ideal tool. The code below is an example. (I have specified the month in the dates so I don't have to use DateTime.ParseExact when setting up the input array).

DateTime[] dates =
{
    DateTime.Parse("jan/01/2009")
    ,DateTime.Parse("feb/01/2009")
    ,DateTime.Parse("feb/12/2009")
    ,DateTime.Parse("mar/02/2009")
    ,DateTime.Parse("mar/12/2009")
    ,DateTime.Parse("mar/22/2009")
};

var datesGroupedByMonthYear = from date in dates
                           group date by date.ToString("MM/yyyy") into groupedDates
                           orderby groupedDates.First() ascending
                           select new { MonthYear = groupedDates.Key, Dates = groupedDates };

string[] monthYears = (from d in datesGroupedByMonthYear select d.MonthYear).ToArray();
int[] number = (from d in datesGroupedByMonthYear select d.Dates.Count()).ToArray();