将数据表中两列的值合并到一个列表中

Question

I am trying to build a list of integers from a data table by combining the data in two of the columns in the data table and getting a distinct list of values.

To get the data table.. i am calling a stored procedure (which i don't have the ability to edit)

After I call my method to return the data table that's returned by the stored procedure.. I want to look at two of the columns in the data table and get a list of values that are in these columns.

The data table returned by the stored procedure looks like this:

I want to get a list of the values in columns MailerKey and BillToKey.
What is the best way to do this? Can I use Linq to do this?

So far I've tried doing:

    using(DataTable dt = getCustomers())
    {
        List<int> MailerKeys = dt.AsEnumerable().Select(x => x.Field<int>("MailerKey")).Distinct().ToList();
        List<int> BillToKeys = dt.AsEnumerable().Select(x => x.Field<int>("BillToKey")).Distinct().ToList();
    }

But how can I now combine the values?

By combine I mean, to get a list that contains the distinct values from both columns.. so eg: I should get back:

275
58
250
50
59
99
55

Answer 1

You could:

• create a HashSet<int> and add both lists to it;
• add one list to the other and use Distinct from System.Linq .

For example:

var a = new[] { 1, 2 }; // Could be any IEnumerale<int>
var b = new[] { 2, 3 }; 

var hash = new HashSet<int>(a);
hash.UnionWith(b);

Console.WriteLine(string.Join(",", hash)); // Prints 1,2,3

Answer 2

You can use Linq to achieve the "combine" step. First concatenate your lists using Concat, then keep only unique values using Distinct.

using(DataTable dt = getCustomers())
{
    var mailerKeys = dt.AsEnumerable().Select(x => x.Field<int>("MailerKey")).Distinct().ToArray();
    var billToKeys = dt.AsEnumerable().Select(x => x.Field<int>("BillToKey")).Distinct().ToArray();

    var combinedDistinctKeys = mailerKeys.Concat(billToKeys).Distinct();
}

Notes:

• 'combinedDistinctKeys' is not yet enumerated, this would occur using ToArray or ToList for example;
• I preferred to use ToArray for the source lists, since I know I will not need List<> features.

For more information about the Concat method from Linq, see: https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.concat?view=net-5.0