Suppose I have list of list. I want to create new list from given list of list such that elements are in order of example given below.
Inputs:-
List<List<int>> l = new List<List<int>>();
List<int> a = new List<int>();
a.Add(1);
a.Add(2);
a.Add(3);
a.Add(4);
List<int> b = new List<int>();
b.Add(11);
b.Add(12);
b.Add(13);
b.Add(14);
b.Add(15);
b.Add(16);
b.Add(17);
b.Add(18);
l.Add(a);
l.Add(b);
Output(list):-
1
11
2
12
3
13
4
14
15
16
And output list must not contain more than 10 elements.
I am currently doing this using foreach inside while but I want to know how can I do this using LINQ.
int loopCounter = 0,index=0;
List<int> o=new List<int>();
while(o.Count<10)
{
foreach(List<int> x in l)
{
if(o.Count<10)
o.Add(x[index]);
}
index++;
}
Thanks.
Use the SelectMany and Select overloads that receive the item's index. That will be used to apply the desired ordering. The use of the SelectMany is to flatten the nested collections level. Last, apply Take to retrieve only the desired number of items:
var result = l.SelectMany((nested, index) =>
nested.Select((item, nestedIndex) => (index, nestedIndex, item)))
.OrderBy(i => i.nestedIndex)
.ThenBy(i => i.index)
.Select(i => i.item)
.Take(10);
Or in query syntax:
var result = (from c in l.Select((nestedCollection, index) => (nestedCollection, index))
from i in c.nestedCollection.Select((item, index) => (item, index))
orderby i.index, c.index
select i.item).Take(10);
If using a C# 6.0 and prior project an anonymous type instead:
var result = l.SelectMany((nested, index) =>
nested.Select((item, nestedIndex) => new {index, nestedIndex, item}))
.OrderBy(i => i.nestedIndex)
.ThenBy(i => i.index)
.Select(i => i.item)
.Take(10);
To explain why Zip alone is not enough: zip is equivalent to performing a join operation on the second collection to the first, where the attribute to join by is the index. Therefore Only items that exist in the first collection, if they have a match in the second, will appear in the result.
The next option is to think about left join which will return all items of the first collection with a match (if exists) in the second. In the case described OP is looking for the functionality of a full outer join - get all items of both collection and match when possible.
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