Question

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Split List into Sublists with LINQ

I’m looking for some way to split an enumerable into three enumerables using LINQ, such that each successive item in the input is in the next sublist in in the sequence. So input

{"a", "b", "c", "d", "e", "f", "g", "h"}

would result in

{"a", "d", "g"}, {"b", "e", "h"}, {"c", "f"}

I’ve done it this way but I’m sure there must be a way to express this more elegantly using LINQ.

var input = new List<string> {"a", "b", "c", "d", "e", "f", "g", "h"};
var list = new List<string>[3];

for (int i = 0; i < list.Length; i++)
    list[i] = new List<string>();

int column = 0;
foreach (string letter in input)
{
    list[column++].Add(letter);
    if (column > 2) column = 0;
}

Answer 1

This is what you are looking for:
(Splits by columns) Modified based on the previous posts

The key difference is in the group by, using mod instead of division.

Also I made it generic so it gives you back the proper type (as opposed to “object typed” code). You can just use type inference with generics.

public static IEnumerable<IEnumerable<T>> SplitColumn<T>( IEnumerable<T> source ) {
    return source
        .Select( ( x, i ) => new { Index = i, Value = x } )
        .GroupBy( x => x.Index % 3 )
        .Select( x => x.Select( v => v.Value ).ToList() )
        .ToList();
}