James Hill James Hill - 4 months ago 14
C# Question

List<T>.ForEach with index

I'm trying to find the LINQ equivalent of the following code:

NameValueCollection nvc = new NameValueCollection();

List<BusinessLogic.Donation> donations = new List<BusinessLogic.Donation>();
donations.Add(new BusinessLogic.Donation(0, "", "", "");
donations.Add(new BusinessLogic.Donation(0, "", "", "");
donations.Add(new BusinessLogic.Donation(0, "", "", "");

for(var i = 0; i < donations.Count(); i++)
{
// NOTE: item_number_ + i - I need to be able to do this
nvc.Add("item_number_" + i, donations[i].AccountName);
}


I was hoping I could use something like:

NameValueCollection nvc = new NameValueCollection();

List<BusinessLogic.Donation> donations = new List<BusinessLogic.Donation>();
donations.Add(new BusinessLogic.Donation(0, "", "", "");
donations.Add(new BusinessLogic.Donation(0, "", "", "");
donations.Add(new BusinessLogic.Donation(0, "", "", "");

donations.ForEach(x => nvc.Add("item_name_" + ??, x.AccountName);


But I've not found a way to determine which iteration the loop is on. Any help would be appreciated!

Answer

LINQ doesn't have a ForEach method, and for good reason. LINQ is for performing queries. It is designed to get information from some data source. It is not designed to mutate data sources. LINQ queries shouldn't cause side effects, which is exactly what you're doing here.

The List class does have a ForEach method, which is what you are using. Because it's not actually in the System.Linq namespace it's not technically a part of LINQ.

There is nothing wrong with the for loop in your question. It would be wrong (from a good practice perspective) to try to change it in the way that you're trying to.

Here is a link that discusses the matter in more detail.

Now, if you want to ignore that advice and use a ForEach method anyway, it's not hard to write one that provides an index to the action:

public static void ForEach<T>(this IEnumerable<T> sequence, Action<int, T> action)
{
    // argument null checking omitted
    int i = 0;
    foreach (T item in sequence)
    {
        action(i, item);
        i++;
    }
}