Create ADO.NET DataView showing only selected Columns

Question

In C# & .NET, can one create a DataView that includes only a proper subset of the DataColumns of a given DataTable?

In terms of relational algebra, one assigns a RowFilter in order to perform a "selection" operation (σ). How would one perform a "projection" operation (π)?

Solution 1

You can't do that, but you can create a copy of the table with only the columns you want :

DataView view = new DataView(table);
DataTable table2 = view.ToTable(false, "FirstColumn", "SecondColumn", "ThirdColumn");

Optionally you can return rows that have distinct values for the selected columns :

DataView view = new DataView(table);
DataTable table2 = view.ToTable(true, "FirstColumn", "SecondColumn", "ThirdColumn");

Solution 2

Well I can't see any reason for "wanting" to do that... Remember, a DataView is just a list of pointers to the rows in the original table, and there is obviously no way to remove columns from the the original table... at least not without affecting every other function utilizing that table... Just only use the columns you want...

Comments

[JaysonFix]

Thank you, Thomas. I'd also like to be able to include calculated columns in "table2". For example, view.ToTable ( "FirstColumn * 2", "SecondColumn > 0", "TRIM(ThirdColumn)" ) .

[Thomas Levesque]

create them in table and select them in ToTable, or add them to table2 after you created it...

[Florian Feldhaus]

You can shorten this by using the DefaultView of the DataTabe: $DataTable.DefaultView.ToTable("FirstColumn", "SecondColumn", "ThirdColumn");

[Smith]

@ThomasLevesque how do I add a condition like FirstColumn = 'comevalue'?

[Thomas Levesque]

@Smith you can add it when you create the view: new DataView(table) { RowFilter = "FirstColumn = 'somevalue'" } (or something like that)