C# Check if any element in an Array Group is Null before comparing length

Question

I have a statement that compares the length of elements in all string arrays.

string[][] allMyArrays= new string[][] { myArray1, myArray2, myArray3 };

lengthMismatch = allMyArrays.GroupBy(x => x.Length).Count() > 1;

However, null exception hits if any of them are null.

How can I get result that lengthMismatch = false if

1. Any, but not all arrays are null
2. One or more array(s) length are not equal

Answer 1

You could use:

bool lengthMismatch = allMyArrays.GroupBy(x => x?.Length ?? int.MinValue).Count() > 1;

On this way you still differrentiate between an empty array and a null array. If all are null this is false as desired.

You could also use an optimized way avoiding GroupBy on the whole array:

int firstLength = allMyArrays.FirstOrDefault()?.Length ?? int.MinValue;
bool anyDifferentLength = allMyArrays.Skip(1)
    .Any(arr => firstLength != (arr?.Length ?? int.MinValue));

Answer 2

Looks like this is one of the cases where LINQ looks cool but not really needed.

Good old foreach might be better from performance and readability perspective, like this:

public static bool IsLengthMismatch(this string[][] arrays)
{
    int? lastLength = -1;

    foreach (var array in arrays)
    {
        if (lastLength != -1 && lastLength != array?.Length)
        {
            return true;
        }

        lastLength = array?.Length;
    }

    return false;
}

Answer 3

Checks if at least one of the arrays is not null using the Any LINQ method.

string[][] allMyArrays = new string[][] { myArray1, myArray2, myArray3 };

bool atLeastOneNotNull = allMyArrays.Any(arr => arr != null);
bool allHaveEqualLength = allMyArrays.All(arr => arr?.Length == allMyArrays[0]?.Length);

bool lengthMismatch = atLeastOneNotNull && !allHaveEqualLength;

// lengthMismatch will be false if any, but not all arrays are null, and one or more array(s) have unequal lengths.