Question

data.Select(object=> string.Format("<a>{0}</a>", object.LinkText))      
.Select(html => string.Format("<div>{0}</div>", html))    
.Aggregate((running, next) => running + next);

I have this query which basically turns some objects into html-markup. What I can´t seem to achieve is that the second select should only be run for every (fixed number) 3 elements in the first select. I wan´t my ouput to be something like this:

<div><a>xxx</a><a>yyy</a><a>zzz</a></div>
<div><a>ååå</a>....</div>

Please help me avoid a for-loop!

Answer 1

To group by 3, use this LINQ query:

    var data = new[] {"quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog"};
    var res = data
        .Select((s, i) => new { Link = string.Format("<a>{0}</a>", s), Index = i })
        .GroupBy(p => p.Index/3)
        .Select(g => string.Format("<div>{0}</div>", string.Join("", g.Select(v => v.Link))));
    foreach (var re in res) {
        Console.WriteLine(re);
    }

The output of this program looks like this:

<div><a>quick</a><a>brown</a><a>fox</a></div>
<div><a>jumps</a><a>over</a><a>the</a></div>
<div><a>lazy</a><a>dog</a></div>

Note how this code uses string.Join instead of a slower Aggregate.
Of course since you use some other objects instead of strings, you will need to replace string.Format("<a>{0}</a>", s) with string.Format("<a>{0}</a>", s.LinkText).