C# – Sorting lists by date and then order by latest

clistsorting

I have a list and would like to sort by date then order by latest date first.

The code below sorts by date:

allFeeds.Sort(delegate(SimplifiedFeedItem p1, SimplifiedFeedItem p2)
                    { return p1.PublishDate.CompareTo(p2.PublishDate); });

                    allFeeds.ForEach(delegate(SimplifiedFeedItem p)
                    { // display list});

How do I then order it by the latest date first (its ordering by the oldest date first currently)?
Thanks

Best Answer

Just change the sign that is returned from DateTime.CompareTo:

allFeeds.Sort(delegate(SimplifiedFeedItem p1, SimplifiedFeedItem p2)
                { return -p1.PublishDate.CompareTo(p2.PublishDate); });

You can make this cleaner using a lambda expression:

allFeeds.Sort((p1, p2) => -p1.PublishDate.CompareTo(p2.PublishDate));

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C# – Case insensitive ‘Contains(string)’

You could use the String.IndexOf Method and pass StringComparison.OrdinalIgnoreCase as the type of search to use:

string title = "STRING";
bool contains = title.IndexOf("string", StringComparison.OrdinalIgnoreCase) >= 0;

Even better is defining a new extension method for string:

public static class StringExtensions
{
    public static bool Contains(this string source, string toCheck, StringComparison comp)
    {
        return source?.IndexOf(toCheck, comp) >= 0;
    }
}

Note, that null propagation ?. is available since C# 6.0 (VS 2015), for older versions use

if (source == null) return false;
return source.IndexOf(toCheck, comp) >= 0;

USAGE:

string title = "STRING";
bool contains = title.Contains("string", StringComparison.OrdinalIgnoreCase);

C# – LINQ’s Distinct() on a particular property

What if I want to obtain a distinct list based on one or more properties?

Simple! You want to group them and pick a winner out of the group.

List<Person> distinctPeople = allPeople
  .GroupBy(p => p.PersonId)
  .Select(g => g.First())
  .ToList();

If you want to define groups on multiple properties, here's how:

List<Person> distinctPeople = allPeople
  .GroupBy(p => new {p.PersonId, p.FavoriteColor} )
  .Select(g => g.First())
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Note: Certain query providers are unable to resolve that each group must have at least one element, and that First is the appropriate method to call in that situation. If you find yourself working with such a query provider, FirstOrDefault may help get your query through the query provider.

Note2: Consider this answer for an EF Core (prior to EF Core 6) compatible approach. https://stackoverflow.com/a/66529949/8155

Best Answer

Related Solutions

C# – Case insensitive ‘Contains(string)’

C# – LINQ’s Distinct() on a particular property

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