Question

When I run this code:

List<string> list = new List<string>();
list.Add("a");
list.Add("b");
list.Add("c");
list.Add("d");

string s = list.Aggregate((total, item) => total += item + ",");

I expect s to be:

a,b,c,d,

but instead, s is:

ab,c,d,

can anyone tell me why it’s not appending a comma between the first and second index?

Thanks

Answer 1

You will find that this works

string s = list.Aggregate(string.Empty, (total, item) => total += item + ",");

You can see why if you test this:

var total = "a";
var item = "b";
var s = total += item + ",";

This results in “ab,”

Using an initial empty seed value for total (either (string)null or string.Empty) will give you the expected result.