CODEWITHSUNDEEP
c#sortinginsert
Jerry
Jerry

Reputation: 1028

How to insert item into list in order?

I have a List of DateTimeOffset objects, and I want to insert new ones into the list in order.

List<DateTimeOffset> TimeList = ...
// determine the order before insert or add the new item

Sorry, need to update my question.

List<customizedClass> ItemList = ...
//customizedClass contains DateTimeOffset object and other strings, int, etc.

ItemList.Sort();    // this won't work until set data comparison with DateTimeOffset
ItemList.OrderBy(); // this won't work until set data comparison with DateTimeOffset

Also, how to put DateTimeOffset as the parameter of .OrderBy()?

I have also tried:

ItemList = from s in ItemList
           orderby s.PublishDate descending    // .PublishDate is type DateTime
           select s;

However, it returns this error message,

Cannot implicitly convert type 'System.Linq.IOrderedEnumerable' to 'System.Collections.Gerneric.List'. An explicit conversion exist (are you missing a cast?)

Upvotes: 39

Views: 92945

Answers (10)

Maxence
Maxence

Reputation: 13329

Using Linq, original list must be already sorted:

List<DateTimeOffset> timeList = new List<DateTimeOffset>()
{
  new DateTimeOffset(2010, 1, 1, 0, 0, 0, TimeSpan.Zero),
  new DateTimeOffset(2011, 1, 1, 0, 0, 0, TimeSpan.Zero), 
  new DateTimeOffset(2012, 1, 1, 0, 0, 0, TimeSpan.Zero), 
  new DateTimeOffset(2013, 1, 1, 0, 0, 0, TimeSpan.Zero)
}; 
Console.WriteLine("Original list:");
timeList.ForEach(dto => Console.WriteLine(dto.ToString("yyyy-MM-dd")));
var newDateTimeOffset = new DateTimeOffset(2011, 6, 12, 0, 0, 0, TimeSpan.Zero);

int index = timeList.TakeWhile(dto => DateTimeOffset.Compare(dto, newDateTimeOffset) < 0).Count();
timeList.Insert(index, newDateTimeOffset);

Console.WriteLine("New list:");
timeList.ForEach(dto => Console.WriteLine(dto.ToString("yyyy-MM-dd")));

Works on all collections, even if they don't have the BinarySearch() method.

Upvotes: 0

Noah Stahl
Noah Stahl

Reputation: 7613

I was curious to benchmark two of the suggestions here, using the SortedSet class vs the List-based binary search insert. From my (non-scientific) result on .NET Core 3.1, it seems the List may use less memory for small (low hundreds) sets, but SortedSet starts winning on both time and memory the larger the set becomes.

(Items were instances of small class with two fields, Guid id and string name)

50 items:

|        Method |     Mean |     Error |    StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|-------------- |---------:|----------:|----------:|-------:|------:|------:|----------:|
|     SortedSet | 5.617 μs | 0.0183 μs | 0.0153 μs | 0.3052 |     - |     - |    1.9 KB |
| SortedAddList | 5.634 μs | 0.0144 μs | 0.0135 μs | 0.1755 |     - |     - |   1.12 KB |

200 items:

|        Method |     Mean |    Error |   StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|-------------- |---------:|---------:|---------:|-------:|------:|------:|----------:|
|     SortedSet | 24.15 μs | 0.066 μs | 0.055 μs | 0.6409 |     - |     - |   4.11 KB |
| SortedAddList | 28.14 μs | 0.060 μs | 0.053 μs | 0.6714 |     - |     - |   4.16 KB |

1000 items:

|        Method |     Mean |   Error |  StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|-------------- |---------:|--------:|--------:|-------:|------:|------:|----------:|
|     SortedSet | 107.5 μs | 0.34 μs | 0.30 μs | 0.7324 |     - |     - |   4.73 KB |
| SortedAddList | 169.1 μs | 0.41 μs | 0.39 μs | 2.4414 |     - |     - |  16.21 KB |

Upvotes: 3

Slate
Slate

Reputation: 3704

I took @Noseratio's answer and reworked and combined it with @Jeppe's answer from here to get a function that works for Collections that implement IList (I needed it for an ObservableCollection of Paths) and type that does not implement IComparable.

    /// <summary>
    /// Inserts a new value into a sorted collection.
    /// </summary>
    /// <typeparam name="T">The type of collection values, where the type implements IComparable of itself</typeparam>
    /// <param name="collection">The source collection</param>
    /// <param name="item">The item being inserted</param>
    public static void InsertSorted<T>(this IList<T> collection, T item)
        where T : IComparable<T>
    {
        InsertSorted(collection, item, Comparer<T>.Create((x, y) => x.CompareTo(y)));
    }

    /// <summary>
    /// Inserts a new value into a sorted collection.
    /// </summary>
    /// <typeparam name="T">The type of collection values</typeparam>
    /// <param name="collection">The source collection</param>
    /// <param name="item">The item being inserted</param>
    /// <param name="comparerFunction">An IComparer to comparer T values, e.g. Comparer&lt;T&gt;.Create((x, y) =&gt; (x.Property &lt; y.Property) ? -1 : (x.Property &gt; y.Property) ? 1 : 0)</param>
    public static void InsertSorted<T>(this IList<T> collection, T item, IComparer<T> comparerFunction)
    {
        if (collection.Count == 0)
        {
            // Simple add
            collection.Add(item);
        }
        else if (comparerFunction.Compare(item, collection[collection.Count - 1]) >= 0)
        {
            // Add to the end as the item being added is greater than the last item by comparison.
            collection.Add(item);
        }
        else if (comparerFunction.Compare(item, collection[0]) <= 0)
        {
            // Add to the front as the item being added is less than the first item by comparison.
            collection.Insert(0, item);
        }
        else
        {
            // Otherwise, search for the place to insert.
            int index = 0;
            if (collection is List<T> list)
            {
                index = list.BinarySearch(item, comparerFunction);
            }
            else if (collection is T[] arr)
            {
                index = Array.BinarySearch(arr, item, comparerFunction);
            }
            else
            {
                for (int i = 0; i < collection.Count; i++)
                {
                    if (comparerFunction.Compare(collection[i], item) <= 0)
                    {
                        // If the item is the same or before, then the insertion point is here.
                        index = i;
                        break;
                    }

                    // Otherwise loop. We're already tested the last element for greater than count.
                }
            }

            if (index < 0)
            {
                // The zero-based index of item if item is found,
                // otherwise, a negative number that is the bitwise complement of the index of the next element that is larger than item or, if there is no larger element, the bitwise complement of Count.
                index = ~index;
            }

            collection.Insert(index, item);
        }
    }

Upvotes: 3

peeyush singh
peeyush singh

Reputation: 33

very simple, after adding data into list

list.OrderBy(a => a.ColumnName).ToList();

Upvotes: 0

noseratio
noseratio

Reputation: 61726

A slightly improved version of @L.B.'s answer for edge cases:

public static class ListExt
{
    public static void AddSorted<T>(this List<T> @this, T item) where T: IComparable<T>
    {
        if (@this.Count == 0)
        {
            @this.Add(item);
            return;
        }
        if (@this[@this.Count-1].CompareTo(item) <= 0)
        {
            @this.Add(item);
            return;
        }
        if (@this[0].CompareTo(item) >= 0)
        {
            @this.Insert(0, item);
            return;
        }
        int index = @this.BinarySearch(item);
        if (index < 0) 
            index = ~index;
        @this.Insert(index, item);
    }
}

Upvotes: 51

Tommy Grovnes
Tommy Grovnes

Reputation: 4156

Modify your LINQ, add ToList() at the end:

ItemList = (from s in ItemList
            orderby s.PublishDate descending   
            select s).ToList();

Alternatively assign the sorted list to another variable

var sortedList = from s in ....

Upvotes: 4

techfun
techfun

Reputation: 953

To insert item to a specific index

you can use:

DateTimeOffset dto;

 // Current time
 dto = DateTimeOffset.Now;

//This will insert the item at first position
TimeList.Insert(0,dto);

//This will insert the item at last position
TimeList.Add(dto);

To sort the collection you can use linq:

//This will sort the collection in ascending order
List<DateTimeOffset> SortedCollection=from dt in TimeList select dt order by dt;

Upvotes: 1

Tim Schmelter
Tim Schmelter

Reputation: 460228

With .NET 4 you can use the new SortedSet<T> otherwise you're stuck with the key-value collection SortedList. 

SortedSet<DateTimeOffset> TimeList = new SortedSet<DateTimeOffset>();
// add DateTimeOffsets here, they will be sorted initially

Note: The SortedSet<T> class does not accept duplicate elements. If item is already in the set, this method returns false and does not throw an exception.

If duplicates are allowed you can use a List<DateTimeOffset> and use it's Sort method.

Upvotes: 15

L.B
L.B

Reputation: 116168

Assuming your list is already sorted in ascending order

var index = TimeList.BinarySearch(dateTimeOffset);
if (index < 0) index = ~index;
TimeList.Insert(index, dateTimeOffset);

Upvotes: 84

levi
levi

Reputation: 3521

You can use Insert(index,object) after finding index you want.

Upvotes: -2

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