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Copy One Column From One DataTable To Another DataTable

Posted on 2006-11-19
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Last Modified: 2010-04-23
I have an application that needs to take column out of a DataTable and insert it into another DataTable.

I have tried:

dtAllTheData.Columns.Add(dtFirst.Columns(3))

but I get an error saying that that column is already part of a dataset.

How do I do this?  I need to create a Single Table that has columns from a series of other tables.

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Question by:lgropper
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Expert Comment

by:Kinger247
ID: 17976072
You could try cloning the column:

Dim DataColumn As DataColumn = dataset.Tables(0).Clone.Columns(0)
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Author Comment

by:lgropper
ID: 17976285
That doesn't work, neither does


Dim MyCol as DataColumn = dataset.Tables(0).Copy.Columns(0)


gives the same Error saying that "" already belongs to dataset.Tables(0)


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Sancler earned 500 total points
ID: 17976383
You could overcome the "belongs to another table" problem on these lines

        Dim dc As DataColumn = dt1.Columns(0)
        dt1.Columns.Remove(dc)
        dt2.Columns.Add(dc)

but it won't produce what (I think) you want.  I imagine that what you actually want is not only the column, but also the data in it.  But the data belongs to a datatable's rows, not to its columns.  So all the above would do would be to put an empty column (with the same properties as the original one) in the second datatable - and, incidentally, get rid of the column and the data in each row for that column in the original datatable.

What you are going to have to do, I think, is create a new column in the second datatable and set its properties the same as those for the column you want to copy.  And then cycle through the rows in the original datatable, creating a new row for the second datatable, and setting the value for that as equal to the equivalent value from the original datatable.  On these lines

       Dim dt2 As New DataTable
       Dim dc As New DataColumn
       With dc
           .ColumnName = dt1.Columns(oldCol).ColumnName
           .DataType = dt1.Columns(oldCol).DataType
           'etcetera for each property you want transferred
       End With
       dt2.Columns.Add(dc)

       For Each dr As DataRow in dt1.Rows
           Dim ndr As DataRow = dt2.NewRow
           ndr(0) = dr(oldCol)
           dt2.Rows.Add(ndr)
       Next

Roger
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Expert Comment

by:Bob Learned
ID: 17978984
You could create a copy of the DataTable, using the Copy method, and then drop the columns that you don't need.

Bob
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Expert Comment

by:Sancler
ID: 17979308
Bob

Agreed - for one column only.  But the question ends "I need to create a Single Table that has columns from a series of other tables" and I don't think you could do that from more than one table.

Roger
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Expert Comment

by:Bob Learned
ID: 17986484
Thanks, Roger, I missed that one.

Bob
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Author Comment

by:lgropper
ID: 18030881
whoops, that should have been Excellent!  thanks a lot!
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