Possible Duplicate:
How can I split an IEnumerable<String> into groups of IEnumerable<string>
I have a list that I would like to break into groups of 10.
If I have an object
List<Person> allPendingPersons that is of length m.
Is there an elegant way in LINQ to break up allPendingPersons into one or more List objects that all have a up to 10 Persons?
You can write your own extension method:
public static IEnumerable<IEnumerable<T>> Partition<T>(this IEnumerable<T> sequence, int size) { List<T> partition = new List<T>(size); foreach(var item in sequence) { partition.Add(item); if (partition.Count == size) { yield return partition; partition = new List<T>(size); } } if (partition.Count > 0) yield return partition; } I explored this in more depth in my blog.
partition = new List<T>(size);
var groups = allPendingPersons.Select((p, index) => new {p,index}) .GroupBy(a =>a.index/10 ); if you want to process IGrouping<,>. If you are looking for List> back you could try
var listOfLists = allPendingPersons.Select((p, index) => new {p, index}) .GroupBy(a => a.index/10) .Select((grp => grp.Select(g => g.p).ToList())) .ToList(); The Reactive Extensions for .NET (Rx) has an extension method that does exactly what you want:
var buffered = allPendingPersons.BufferWithCount(10); If you want to do it using LINQ you could do this:
var buffered = allPendingPersons .Select((p, i) => new { Group = i / 10, Person = p }) .GroupBy(x => x.Group, x => x.Person) .Select(g => g.ToArray()); These should be of some assistance.
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One very popular answer is to check out Jon Skeet's MoreLinq, in particular, the Batch function, which not only does what you are asking for, but also lets you specify a return selector!
Batch, see source hereIt's not the most efficient technique, but this will produce an IEnumerable<IEnumerable<Person>> sequence, with each inner sequence containing ten elements:
var query = allPendingPersons.Select((x, i) => new { Value = x, Group = i / 10 }) .GroupBy(x => x.Group, (k, g) => g.Select(x => x.Value)); And if the result really does need to be a list-of-lists rather than a simple sequence then you can create a List<List<Person>> instead by adding in a couple of ToList calls:
var query = allPendingPersons.Select((x, i) => new { Value = x, Group = i / 10 }) .GroupBy(x => x.Group, (k, g) => g.Select(x => x.Value).ToList()) .ToList(); 
x => x.Value instead of (k, g) => g.Select(x => x.Value).Try an iterator block:
public static IEnumerable<List<Person>> AsGroups(this List<Person> persons) { var buf = new List<Person>(10); for (int i = 0; i<persons.Count i++;) { buf.Add(persons[i]); if (i%10 == 0 && buf.Count > 0) { yield return buf; buf = new List<Person>(10); } } yield return buf; } Is there an elegant way in LINQ
The elegant way is not very performant. Here is a more performant way...
public static List<List<T>> Chunk<T>( this List<T> theList, int chunkSize ) { if (!theList.Any()) { return new List<List<T>>(); } List<List<T>> result = new List<List<T>>(); List<T> currentList = new List<T>(); result.Add(currentList); int i = 0; foreach(T item in theList) { if (i >= chunkSize) { i = 0; currentList = new List<T>(); result.Add(currentList); } i += 1; currentList.Add(item); } return result; } 