How to get Max String Length in every Column of a Datatable

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?

Solution 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();

Solution 2

With c# 6, you can prevent the exception by adding val?.Length

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

Comments

[MsBao]

That gets the length of the longest string in the whole table. I need the lengths of the longest strings in every column.

[Fandango68]

Don't you mean IEnumerable? Enumerable is undefined in C#

[Mehdi Anis]

Code from @roncansan works great. However how can I get {ColumnName, MaxLength} pair in the "var maximumLengthForColumns"? OR Is it "Guranteed" that the MaxLength values in the "var maximumLengthForColumns" will be in exact order of the Columns in the table. Thanks.