Question

I have a DataTable object. Every column is of type string.

Using LINQ, how can I get the maximum string length for every column?

Answer 1

The maximum string length for the whole table:

int? maxStringLength = dataTable.AsEnumerable()
    .SelectMany(row => row.ItemArray.OfType<string>())
    .Max(str => str?.Length);

If you want maximum string length for each column, you could do:

List<int?> maximumLengthForColumns = 
   Enumerable.Range(0, dataTable.Columns.Count)
       .Select(col => dataTable.AsEnumerable()
            .Select(row => row[col]).OfType<string>()
            .Max(val => val?.Length)
       ).ToList();