C# Best way to remove all datatables apart from one

Question

I want to delete all datatables in a dataset apart from one. I've tried this :-

        foreach (DataTable table in DtSet.Tables)
        {
            if (table.TableName != "tblAccounts")
            {
                DtSet.Tables.Remove(table);
            }
        }

but I get a

"Collection was modified; enumeration operation may not execute." error

.

score 3 · Accepted Answer · answered Jan 14 '13 at 22:49

3

You cannot modify a collection during enumeration. But you could use a for-loop:

for (int i = DtSet.Tables.Count - 1; i >= 0; i--)
{
    var table = DtSet.Tables[i];
    if (table.TableName != "tblAccounts")
        DtSet.Tables.Remove(table);
}

answered Jan 14 '13 at 22:49

Tim Schmelter

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score 2 · Answer 2 · answered Jan 14 '13 at 23:03

2

Just throwing this out there as it is untested but has no loops.

var accounts = DtSet.Tables["tblAccounts"];
DtSet.Tables.Clear();
DtSet.Tables.Add(accounts);

answered Jan 14 '13 at 23:03

Austin Salonen

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Nice idea +1, however, `Clear` is not for free. – Tim Schmelter Jan 14 '13 at 23:21
"in code that I wrote anyway" -- ;-). The string indexer probably has a loop as well. – Austin Salonen Jan 14 '13 at 23:46

score 1 · Answer 3 · answered Jan 14 '13 at 22:50

You'll get this anytime you try to modify a collection during a foreach. It has to do with the way the collection is iterated through.

You can do it a couple ways - one way is to determine the tables you want to remove while you're in the loop, then afterward, go back and remove them. I think the following will work:

var tablesToRemove = new List<DataTable>();
foreach (DataTable table in DtSet.Tables)
{
    if (table.TableName != "tblAccounts")
    {
        tablesToRemove.Add(table);
    }
}

foreach (DataTable table in tablesToRemove)
{
    DtSet.Tables.Remove(table);
}

Tim's answer will definitely run faster since you're only looping through once. This way gets you the benefit of being able to debug and see exactly which tables you'll be removing before removing them. But I'd probably do it Tim's way. — Joe Enos, Jan 14 '13 at 22:52

C# Best way to remove all datatables apart from one

3 Answers3