What is LINQ operator to perform division operation on Tables?

Question

To select elements belonging to a particular group in Table, if elements and their group type are contained in one table and all group types are listed in another table we perform division on tables. I am trying LINQ query to perform the same operation. Please tell me how can I do perform it?

Answer 1

Apparently from the definition of that blog post you'd want to intersect and except.

Table1.Except(Table1.Intersect(Table2));

or rather in your case I'd guess

Table1.Where(d => !Table2.Any(t => t.Type == d.Type));

not so hard.

I don't think performance can be made much better, actually. Maybe with a groupby.

Table1.GroupBy(t => t.Type).Where(g => !Table2.Any(t => t.Type == g.Key)).SelectMany(g => g);

this should be better for performance. Only searches the second table for every kind of type once, not for every row in Table1.

Answer 2

It's a bit difficult to determine exactly what you're asking. But, it sounds like you are looking to determine the elements that are common in two tables or streams. If so, I think you want Intersect.

Take a look here

It works something like this:

int[] array1 = { 1, 2, 3 };
int[] array2 = { 2, 3, 4 };
var intersect = array1.Intersect(array2);

Returns 2 and 3.

The opposite of this would be Except().