Linq to SQL: Get number of consecutive daily views
I have a table that rec开发者_运维技巧ords when a user views a page. The table looks something like this:
ID | Date
1 | 01/01/10 00:00:01.000
2 | 03/01/10 00:00:01.000
3 | 03/01/10 00:00:02.000
4 | 04/01/10 00:00:01.000
5 | 05/01/10 00:00:01.000
6 | 05/01/10 00:00:02.000
7 | 05/01/10 00:00:03.000
Using Linq-to-SQL I want to count the last group of consecutive days a page was viewed, but of course I'm not sure how I would go about doing this. For example, running the query on the data above should return 3.
Any help would be muchly appreciated :)
This is the test data. I added 6th Oct at the end of list to make sure the result only pick up last consecutive date set.
List<DateTime> viewDates = new List<DateTime>();
viewDates.Add(new DateTime(10, 10, 1));
viewDates.Add(new DateTime(10, 10, 3));
viewDates.Add(new DateTime(10, 10, 3));
viewDates.Add(new DateTime(10, 10, 4));
viewDates.Add(new DateTime(10, 10, 5));
viewDates.Add(new DateTime(10, 10, 5));
viewDates.Add(new DateTime(10, 10, 5));
viewDates.Add(new DateTime(10, 10, 6));
First, we need to find out the last consecutive date:
var lastConsecutiveDate = viewDates
.Distinct()
.Reverse()
.SkipWhile(distinctDate => viewDates.Where(viewDate => (viewDate.Date == distinctDate.Date)).Count() < 2).FirstOrDefault();
We have 2 choices here, to use foreach
or LINQ
? foreach
is more readable compared to LINQ
. I will show both implementations.
This is the implementation for foreach
:
var consecutiveDates = new List<DateTime>();
foreach (var item in viewDates.Where(viewDate => viewDate <= lastConsecutiveDate).Distinct().OrderByDescending(a => a.Date))
{
//break if datediff is not 1
int count = consecutiveDates.Count;
if ((count > 0) && (consecutiveDates[count - 1].Date.AddDays(-1) != item.Date))
{
break;
}
consecutiveDates.Add(item);
}
This is the implementation for LINQ
, less readable:
var consecutiveDates = viewDates
.Where(viewDate => viewDate <= lastConsecutiveDate)
.Distinct()
.OrderByDescending(viewDate => viewDate.Date)
.Aggregate
(
new { List = new List<DateTime>() },
(result, viewDate) =>
{
int count = result.List.Count;
if ((count > 0) && (result.List[count - 1].Date.AddDays(-1) != viewDate.Date))
{
return new { result.List };
}
result.List.Add(viewDate);
return new { result.List };
},
a => a.List
);
Console.WriteLine(consecutiveDates.Count());
will print out "3".
I am expecting more refactoring on my code, but I am off for break.
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