Create a new List based on another two Lists C#-CodePudding

i'm trying to write a desktop app using c# .NET , but currently i'm stuck in the following problem:

Assume you have two Lists:

List1=[1,2,3,4]

List2=[1,4,1,3]

And i want a new list that is filled with "n" zeros between two consecutive elements of list1, been "n" the "i" element of list2, the new list should look like this:

List3=[1,0,2,0,0,0,0,3,0,4,0,0,0]

My Code:

  List<int> idID = new List<int>();
            idID.Add(1);
            idID.Add(2);
            idID.Add(3);
            idID.Add(4);
            List<int> Nevent = new List<int>();
            Nevent.Add(1);
            Nevent.Add(4);
            Nevent.Add(1);
            Nevent.Add(3);

            int total = Nevent.Count;



            for (int j = 0; j < total; j  )
            {
                for (int i = 1; i <= Nevent[j]; i  )
                {                
                    idID.Insert(i, 0);    //modify (____,0) of this line???
                }

            }


            string IDS = String.Join(",", idID);
            Console.WriteLine(IDS);

I think that i should change the part with idID.Insert(i, 0); and replace the i with some kind of sequence form like N0,N0 N1,N0 N1 N2,... been Ni the i element of list2 (that i name Nevent in the code) but i do not know how to do that.

How should I proceed? or there is a better way to achive what i want? Thank you in advance.

CodePudding user response：

If we assume the lists are the same length, you can make use of Zip to zip the 2 arrays together, and then a bit of LINQ to build up and select the resulting array

var result = idID.Zip(Nevent, 
                      (x,y) => new[]{ x }.Concat(Enumerable.Repeat(0,y)) )
                 .SelectMany(x => x);

result is

1,0,2,0,0,0,0,3,0,4,0,0,0

Live example: https://dotnetfiddle.net/PvtOVv

If you want/need to have result as a list just tag ToList() on the end

CodePudding user response：

Create new list, and treat idID and Nevent as input only. With LINQ we can use Enumerable.Repeat, otherwise we would have to use inner loop to add zeros.

using System.Linq;

...

List<int> result = new List<int>();

for (int j = 0; j < idID.Count; j  )
{
    result.Add(idID[j]);
    result.AddRange(Enumerable.Repeat(0, Nevent[j]));
}

CodePudding user response：

Another approach is to process the list backwards. Like this the inserted zeroes do not alter the indexes of elements to be processed.

var idID = new List<int> { 1, 2, 3, 4 };
var Nevent = new List<int> { 1, 4, 1, 3 };

for (int i = idID.Count - 1; i >= 0; i--) {
    for (int n = 0; n < Nevent[i]; n  ) {
        idID.Insert(i   1, 0);
    }
}

Console.WriteLine(String.Join(",", idID));

prints

1,0,2,0,0,0,0,3,0,4,0,0,0

CodePudding user response：

Add .ToList() with answer of @Jamiec