Linq Order by a specific number first then show all rest in order

Question

If i have a list of numbers:

1,2,3,4,5,6,7,8

and I want to order by a specific number and then show the rest. For example if i pick '3' the list should be:

3,1,2,4,5,6,7,8

Looking for linq and c#. Thank you

Solution 1

You can use a comparison in OrderBy or ThenBy to perform a conditional sorting.

list.OrderByDescending(i => i == 3).ThenBy(i => i);

I use OrderByDescending because i want matching results first(true is "higher" than false).

Solution 2

A couple of answers already sort the last few numbers (which may be correct since you're only showing an already sorted list). If you want the "unselected" numbers to be displayed in their original, not necessarily sorted order instead of sorted, you can instead do;

int num = 3;
var result = list.Where(x => x == num).Concat(list.Where(x => x != num));

As @DuaneTheriot points out, IEnumerable's extension method OrderBy does a stable sort and won't change the order of elements that have an equal key. In other words;

var result = list.OrderBy(x => x != 3);

works just as well to sort 3 first and keep the order of all other elements.

Solution 3

Maybe something like this:

List<int> ls=new List<int>{1,2,3,4,5,6,7,8};
int nbr=3;
var result= ls.OrderBy (l =>(l==nbr?int.MinValue:l));

Solution 4

public static IEnumerable<T> TakeAndOrder<T>(this IEnumerable<T> items, Func<T, bool> f)
{       
    foreach ( var item in items.Where(f))
        yield return item;
    foreach (var item in items.Where(i=>!f(i)).OrderBy(i=>i))
        yield return item;
}


var items = new [] {1, 4, 2, 5, 3};
items.TakeAndOrder(i=> i == 4);

View more solutions

Comments

[Duane Theriot]

You can accomplish the same thing with list.OrderBy(i => i != 3).

[Tim Schmelter]

@cracker: change OrderByDescending to OrderBy or i == 3 to i != 3

[Pranesh Janarthanan]

if want to sort string column myDataList.OrderByDescending(i => i.StringColumnValue[0] == filterStringValue[0]).ToList() . i used your logic here. Based on filter starting letter, those results are displayed in the order with same starting letter

[Kevin]

Sorry for the necro comment, but this isn't a good idea. Because if the list contains any entries of int.MinValue, this approach isn't going to work.

[Manish Joisar]

So integer collection works but object collection is not working, am i missing anything here ? object.OrderByDescending(m => m.id== 298).ThenBy(x => x.CreatedOn)

[Tim Schmelter]

@ManishJoisar: it works the same way. The point is that m.id== 298 returns a bool which can be true or false and OrderByDescending will yield the true-values first. Maybe the reason why you think that it doesn't work is somethingelse. Create a question, so others can help.

[Manish Joisar]

stackoverflow.com/questions/70213940/…