CODEWITHSUNDEEP
c#linq
Kacper Werema
Kacper Werema

Reputation: 448

LINQ - Decide which date is the oldest for each record

Hey i got a list having many records inside, there are 3 DateTime inside (nullable). What i need is to get a LINQ expression determining which one of this three is the latest then select that record and check again. Here is the code how i created the List.

List<ActivityJoinUserTopicVote> ActivityList = new List<ActivityJoinUserTopicVote>();
foreach (var p in postdate)
{
    ActivityList.Add(new ActivityJoinUserTopicVote(p.R_Posted, p.Forum_id, p.R_Posted_By, p.R_Message, p.Reply_ID, p.Topic_ID, p.User));
}
foreach (var v in votedate)
{
    ActivityList.Add(new ActivityJoinUserTopicVote(v.data, v.Topic_ID, v.vote, v.Member_ID, v.Vote_Member_ID));
}
foreach (var t in topicdate)
{
    ActivityList.Add(new ActivityJoinUserTopicVote(t.T_date, t.Forum_id, t.T_Originator, t.T_Replies, t.T_ukaz, t.Topic_ID, t.User, t.T_Url, t.T_subject));
}
return ActivityList;

Before returning the ActivityList i need it to determine which one was the most recent and sort it this way. Maybe i could do this somehow while creating the list? The problem is i got 3 different columns inside i need to check in (R_Posted, data and T_date)

Upvotes: 0

Views: 189

Answers (3)

fubo
fubo

Reputation: 45947

replace 

return ActivityList;

with 

return ActivityList.OrderByDescending(x =>  x.data.HasValue ? x.data : ( x.R_Posted.HasValue ? x.R_Posted : x.T_date)).ToList();

or 

return ActivityList.OrderByDescending(x => new DateTime?[]{ x.data, x.R_Posted, x.T_date}.Max()).ToList();

to return the ActivityList sorted by the date fields descending

Upvotes: 2

Zein Makki
Zein Makki

Reputation: 30022

Get the maximum of 3 dates using ticks, and sort by that value:

Helper:

private long MaxOfThreeDate(DateTime? date1, DateTime? date2, DateTime? date3)
{
    long max1 = Math.Max(date1.GetValueOrDefault().Ticks, date2.GetValueOrDefault().Ticks);

    return Math.Max(max1, date3.GetValueOrDefault().Ticks);
}

Usage:

return ActivityList.OrderByDescending(x => MaxOfThreeDate(x.data, x.R_Posted, x.T_date)).ToList();

Upvotes: 3

riteshmeher
riteshmeher

Reputation: 874

You can get the most recent one using this

var list = ActivityList.OrderByDescending(x=>x.Date).First();

Upvotes: 1

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