Question

How to convert List<string> to List<int> where empty or null string to be converted as 0 using LINQ in C#

Following LINQ statements will convert the List<sting> to List<int> but do these statements work for above mentioned scenario

listofIDs.Select(int.Parse).ToList()

var intList = stringList.Select(s => Convert.ToInt32(s)).ToList()

Answer 1

Here’s my pitch:

        var stringlist = new List<String> { "1", "2", "", null };
        var intList = stringlist.Select(s => { int i; return int.TryParse(s, out i) ? i : 0; }).ToList();
        Debug.Print("{0},{1},{2},{3}", intList[0], intList[1], intList[2], intList[3]);

Test output: 1,2,0,0

Not dissimilar to the IsNullOrWhiteSpace suggestion. However, it’s safer than just using int.Parse unguarded, which will throw an exception if given invalid input.

A suggestion for you: TDD! Get familiar with one of the many .NET testing frameworks. You can answer questions like yours with another 2-3 lines of code.