Get Distinct String List From DataTable

Question

To reduce the amount of code, is it possible to combine this in one line - where I convert a DataTable column into a string list, but I only want the distinct items in that list (there are multiple columns, so sometimes columns will have multiple values, where one won't):

List<string> column1List = returnDataTable.AsEnumerable().Select(x => x["Column1"].ToString()).ToList();
var distinctColumn1 = (from distinct1 in column1List select distinct1).Distinct();

The above works, but is an extra line. Since the distinct is an option on the list, I did try:

List<string> column1List = (returnDataTable.AsEnumerable().Select(x => x["Column1"].ToString()).ToList()).Distinct();

However, that errors, so it appears that distinct can't be called on a list being converted from a DataTable (?).

Just curious if it's possible to convert a DataTable into a string list and only get the distinct values in one line. May not be possible.

Answer 1

Distinct returns IEnumerable<TSource> in your case it returns IEnumerable<String> and you are trying to get the List<String> in the output.

You need to change the code from

List<string> column1List = (returnDataTable.AsEnumerable().Select(x => x["Column1"].ToString()).ToList()).Distinct();


List<string> column1List = (returnDataTable.AsEnumerable().Select(x => x["Column1"].ToString()).Distinct().ToList();

Answer 2

使用System.Linq您可以使用类似这样的东西

my_enumerable.GroupBy(x => x.Column1).Select(x => x.First).ToList()