Question

I have loaded a txt comma delimited into multiple lists. For example

static public void File()    
{    
    var order_no = new List<String>();    
    var quantity = new List<String>();    
    order_no.Add(fields[0]);    
    quantity.Add(fields[1]);    
}       

Now what i am trying to is in a loop while the same order is found down the list and the quantity is null then update the quantity in the previous.

For example

order NO : 1 quantity: null

order NO : 5 quantity: 2

order no : 1 quantity: 1

what it should do is to update the quantity in the first value to 1.

How can i accomplish that?

Answer 1

Personally i would prefer a Dictionary<String, String> instead since these pairs belong logically together(one quantity per order). But ok…

You could group by order_no and select only one not-null value(if any):

var orderGroups = order_no
    .Select((order, index) => new { 
         order, index,
         quantity = quantity.ElementAtOrDefault(index)
     })
    .GroupBy(x => x.order)
    .Where(g => g.Count() > 1);
foreach(var og in orderGroups)
{
    var firstNotNull = og.FirstOrDefault(x => x.quantity != null);
    if (firstNotNull != null)
    {
        var allIndices = og.Select(x => x.index);
        foreach (int index in allIndices)
            quantity[index] = firstNotNull.quantity;
    }
}

If you don’t want the first not-null quantity but the highest one, change these lines:

var firstNotNull = og.Where(x => x.quantity != null)
                     .OrderByDescending(x => int.Parse(x.quantity))
                     .FirstOrDefault();