Compare two lists and return common entries

I have a list of vendors. I also have a list of vendor ids.

    public List<SAP_Vendor> Vendors { 开发者_如何学编程get; set; }
    public List<string> SubcontractVendorIDs { get; set; }

I want to return a List<SAP_Vendor> of the vendors whose ids are in the SubcontractVendorIDs list.

List<SAP_Vendor> SubcontractVendors = Vendors.Select(??).ToList();

or

List<SAP_Vendor> SubcontractVendors = Vendors.Where(??).ToList();

Use the Contains() method in the Where() predicate:

List<SAP_Vendor> SubcontractVendors = Vendors.Where(v=> SubcontractVendorIDs.Contains(v.VendorID)).ToList();

You can perform an inner join:

var query = from vendor in Vendors
            join id in SubcontractVendorIDs on vendor.ID equals id
            select vendor;

List<SAP_Vendor> subcontractVendors = query.ToList();

List<SAP_Vendor> SubcontractVendors = Vendors.Where(v => SubcontractVendorIDs.Contains(v.Id)).ToList(); 

Do you need to be using Lists? With LINQ, it's usually best to pass around IEnumerables and only convert to a list when you actually need the data.

As for your actual question, just use the Contains method.

Vendors.Where(v => SubcontractVendorIDs.Contains(v.Id));

List<SAP_Vendor> SubcontractVendors = Vendors.Where(x => SubcontractVendorIDs.Any(y => x == y)).ToList();

One of several ways to do this... Would be faster with a Dictionary or a sorted list