What's the LINQ'ish way to do this

Question

Say, I have an array of lists, and I want to get a count of all of the items in all of the lists. How would I calculate the count with LINQ? (just general curiosity here)

Here's the old way to do it:

List<item>[] Lists = // (init the array of lists)
int count = 0;
foreach(List<item> list in Lists)
  count+= list.Count;
return count;

How would you LINQify that? (c# syntax, please)

Answer 1

Use the Sum() method:

int summedCount = Lists.Sum(l => l.Count);

Answer 2

I like @jrista's answer better than this but you could do

int summedCount = Lists.SelectMany( x => x ).Count();

Just wanted to show the SelectMany usage in case you want to do other things with a collection of collections.

Answer 3

And if you want to be fancy

 int summedCount = Lists.Aggregate(0, (acc,list) => acc + list.Count);

But the first answer is definitely the best.