how do I check if an entity is the first element of a foreach loop

Question

Say I have a foreach loop.

I have to do something with the first object of the loop that I don't have to do with any of the other objects.

How do I check if the item that's currently in the loop is the first object.

Answer 1

Something like this:

bool first = true;

foreach(var item in items)
{
    if (first)
    {
        item.firstStuff();
        first = false;
    }
    item.otherStuff();
}

Answer 2

bool first = true;
foreach(var foo in bar)
{
  if (first)
  {
    // do something to your first item
    first = false;
  }
  // do something else to the rest
}

Answer 3

Can't think of anything but

var processedFirst = false;
foreach(var x in items) {
    if(!processedFirst) {
        ProcessFirst(x);
        processedFirst = true;
    }

Answer 4

Here's a performant solution:

using (var erator = enumerable.GetEnumerator())
{
    if (erator.MoveNext())
    {
        DoActionOnFirst(erator.Current);

        while (erator.MoveNext())
            DoActionOnOther(erator.Current);
    }
}

EDIT: And here's a LINQ one:

if (enumerable.Any())
    {
        DoActionOnFirst(enumerable.First());

        foreach (var item in enumerable.Skip(1))
            DoActionOnOther(item);
    }

EDIT: If the actions on the items have signatures assignable to Func<TItem, TResult>, you can do:

enumerable.Select((item, index) => index == 0 ? GetResultFromFirstItem(item) : GetResultFromOtherItem(item));

Answer 5

There are several ways that you could do that.

1. Use a for loop instead
2. Set a Boolean flag
3. Use Linq to get the list.First() and then foreach over list.Skip(1)

Answer 6

try this one

bool IsFirst = true;

foreach(DataRow dr in dt.Rows)
{
    if (IsFirst)
    {
        // do some thing
        IsFirst = false;
    }    
}

Answer 7

This is more of a general solution for getting index along with each object in an array. Should work testing if it's the first.

        List<String> entries = new List<string>();
        entries.Add("zero");
        entries.Add("one");
        entries.Add("two");

        Dictionary<int, String> numberedEntries = new Dictionary<int, string>();
        int i = 0;
        entries.ForEach(x => numberedEntries.Add(i++, x));
        foreach (KeyValuePair<int, String> pair in numberedEntries) {
            Console.WriteLine(pair.Key + ": " + pair.Value);
        }

In this setup, the Key of the KeyValuePair is the index and the value is the object at that index, in my example a string, but any object could be placed their. It adds a little overhead, but can be used to determine any object in the list's index when needed.