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);
                }
            }