Compare 2 datatable columns and delete missing columns

Question

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<table7_ref.Columns.Count; p++)
{
string colxname = table7_ref.Columns[p].ToString();
if (!table7.Columns.Contains(colxname))
{
table7_ref.Columns.Remove(colxname);
}
}

Vulpes · 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); } }

Vulpes · Answer

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 Shariff · Answer

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 :)

Farhan Shariff · Answer

yeah have to take p = total count I was thinking where I was going wrong

Farhan Shariff · Answer

No its not working

Khan Abrar Ahmed · Answer

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 (ColumnD) == table2.Field (ColumnD) select table1;

Farhan Shariff · Answer

it just creates columns but the rows for each columns are not copied

Khan Abrar Ahmed · Answer

Hiyou cant modify the list while in the loop can you please add / DataTable Newtable7_ref = new DataTable(); for(int p=0; p { string colxname = table7_ref.Columns[p].ToString(); if (table7.Columns.Contains(colxname)) { //new table variable and the maching column Newtable7_ref.Columns.add(colxname); } } after that assign the value table7_ref =Newtable7_ref;