Question

Lets say I have List<string> = new List<string>() {"20","26","32"}

I want to create a new List based on the first number in the previous list and it should have the same number of elements in it. I will be adding a certain number to that first number and so on and so on. As an example, using 6 as the number to add I would get 20,26,32. The resulting list will be List. The number 6 is a class wide property.

The issue comes if I have a list of “N”,”N”,”32″

I need to produce the same list of 20,26,32 but I have to use the last number to work out the others.

If I had “N”,”26″,”N” I would have to use the middle number to work out the others.

The N represents no data in the input list and it will always be this character

In summary, I need to produce a new list with the same number of elements as the input list and it must take the first or next numerical element to produce the resulting list using a specified number to add/subtract values to.

I wondered if LINQ’s aggregate function might be able to handle it but got a bit lost using it.

Examples:

"20","26","32" = 20,26,32
"N","26","32" = 20,26,32
"N","N","32" = 20,26,32
"20","26","N" = 20,26,32

Answer 1

What about something like this:

var n = 6;

List<string> strList = new List<string>() {"20","26","32"}; 
// list can also be {null, "26", null} , {null, "N", "32"} , 
//                  {"N", "26", null } etc...

var list = strList.Select(s =>
{
   int v;
   if(string.IsNullOrEmpty(s) || !int.TryParse(s,out v))
      return (int?)null;
   return v;
});

var firstValidVal = list.Select((Num, Index) => new { Num, Index })
                        .FirstOrDefault(x => x.Num.HasValue);
if(firstValidVal == null)
    throw new Exception("No valid number found");

var bases = Enumerable.Range(0, strList.Count).Select(i => i * n);
int startVal = firstValidVal.Num.Value - bases.ElementAt(firstValidVal.Index);

var completeSequence = bases.Select(x => x + startVal);