Compare 2 datatable columns and delete missing columns

Farhan Shariff

I have two datatables

Table7_ref

A	B	C	D	E	F	G	H	I	J
1	2	3	4	6	8	9	0	-	8

Table7

A	B	C	D
13	11	144	12

Output
table7_ref

A	B	C	D
1	2	3	4

What is the mistake I am doing

for(int p=0; p {
string colxname = table7_ref.Columns[p].ToString();
if (!table7.Columns.Contains(colxname))
{
table7_ref.Columns.Remove(colxname);
}
}

8 Replies

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Vulpes12y ago
Accepted answer
You'll need to iterate backwards through the Columns collection to make multiple deletions.

Try this:

for(int p = table7_ref.Columns.Count - 1; p >= 0; p--)
{
string colxname = table7_ref.Columns[p].ColumnName;
if (!table7.Columns.Contains(colxname))
{
table7_ref.Columns.RemoveAt(p);
}
}
Farhan Shariff12y ago
ahh How could I not remember it :( last time it was while removing rows... Yeah I remember it now you had told me that anyways Thank you :)
Vulpes12y ago
The trouble is that, when you iterate forwards through the collection, each time you remove an element the indices of the later elements all move down 1.

However, you can still ensure that you'll examine all the elements by reducing the control variable by 1 each time you make a removal. So this should also work:

for(int p=0; p
{
string colxname = table7_ref.Columns[p].ToString();
if (!table7.Columns.Contains(colxname))
{
table7_ref.Columns.Remove(colxname);
p--;
}
}
Farhan Shariff12y ago
yeah have to take p = total count I was thinking where I was going wrong
Farhan Shariff12y ago
No its not working
Khan Abrar Ahmed12y ago
Hi try to use linq

var matched = from table1 in Table7_ref.AsEnumerable()
join table2 in Table7.AsEnumerable() on table1.Field("ColumnA") equals table2.Field("ColumnA")
where table1.Field("ColumnB") == table2.Field("ColumnB") || table1.Field("ColumnC") == table2.Field("ColumnC") || table1.Field