Error when converting splitted string

Question

I have a string that I take from a property of an object. I split IT into a list of strings that I then want to cast into a list of ints.

This is what the code looks like:

TheListOfInts = s.TheListOfStrings
  .Split(',')
  .ToList()
  .Select(g => Convert.ToInt32(g))
  .ToList();

I'm getting an error

Input string was not in a correct format.

The problem is that sometimes TheListOfStrings is ;null; and I think that's what triggers the error. What can I add in the lambda to take into account the possibility of a null string?

Answer 1

When parsing a string to an int you want to use int.TryParse to make sure it won't throw an exception. In linq you can do it this way:

var result = s.TheListOfStrings.Split(',')
              .Select(i => (int.TryParse(i, out var value), value))
              .Where(pair => pair.Item1) // remove items that failed to be parsed
              .Select(pair => pair.value) // take the parsed value
              .ToList();

This fixes the cases of the empty items from the split (you can still add the RemoveEmptyEntries flag) and also, in case an item is not a valid integer it won't parse it.

Notice that the first ToList() that you added is not needed.

---

As you are using a pre C# 7.0 version then you should:

int value;
var result = s.TheListOfStrings.Split(',')
              .Select(i => new { Succeeded = int.TryParse(i, out value), Value = value })
              .Where(pair => pair.Succeeded) // remove items that failed to be parsed
              .Select(pair => pair.Value) // take the parsed value
              .ToList();

Difference:

• Anonymous type instead of named tuples
• out instead of out var

---

In your question you stated: The problem is that sometimes TheListOfStrings is null and I think that's what triggers the error.

This will not be the cause for the error as if it was you would have received a NullReferenceException.

To cope with that you can:

1. Use the ?. operator (and then the result might be null instead of an empty collection.

2. Check if it is null:

   var result = s.TheListOfStrings == null ? 
                    Enumerable.Empty<int> () : 
                    /*The linq query above*/;
   

Answer 2

int x;
var TheListOfInts = s.TheListOfStrings.Split(',').Select(g => Int32.TryParse(g, out x) ? x : 0).ToList();

Use tryparse, and catch whether g is a valid integer and you can set a default if not. (I put the default to 0);