Getting pair-set using LINQ

When i have a list

IList<int> list = new List<int>();
list.Add(100);
list.Add(200);
list.Add(300);
list.Add(400);
list.Add(500);

What is the way to extract a pairs

Example : List elements {100,200,300,400,500}

Expected Pair : { {100,200} ,{200,300} ,{300,400} ,{400,500} }

The most elegant way with LINQ: list.Zip(list.Skip(1), Tuple.Create)

A real-life example: This extension method takes a collection of points (Vector2) and produces a collection of lines (PathSegment) needed to 'join the dots'.

static IEnumerable<PathSegment> JoinTheDots(this IEnumerable<Vector2> dots)
{
    var segments = dots.Zip(dots.Skip(1), (a,b) => new PathSegment(a, b));
    return segments;
}

This will give you an array of anonymous "pair" objects with A and B properties corresponding to the pair elements.

var pairs = list.Where( (e,i) => i < list.Count - 1 )
                .Select( (e,i) => new { A = e, B = list[i+1] }  );

You can use a for loop:

var pairs = new List<int[]>();
for(int i = 0; i < list.Length - 1; i++)
    pairs.Add(new [] {list[i], list[i + 1]);

You can also use LINQ, but it's uglier:

var pairs = list.Take(list.Count - 1).Select((n, i) => new [] { n, list[i + 1] });

EDIT: You can even do it on a raw IEnumerable, but it's much uglier:

var count = list.Count();
var pairs = list
    .SelectMany((n, i) => new [] { new { Index = i - 1, Value = n }, new { Index = i, Value = n } })
    .Where(ivp => ivp.Index >= 0 && ivp.Index < count - 1)    //We only want one copy of the first and last value
    .GroupBy(ivp => ivp.Index, (i, ivps) => ivps.Select(ivp => ivp.Value));

Getting pair-set using LINQ

Related

Recent Posts