c# - Foreach 循环（包含 LINQ）性能提升

Question

我希望简化以下包含 foreach 循环的代码，以最小化迭代和/或提高性能，因为每次迭代都会创建 LINQ 和集合：

foreach (Contact contact in Contacts) // phone contacts, around 500-1000
{
    IEnumerable<ContactEmailAddress> emails = contact.EmailAddresses; // each has multiple emails

    foreach (Friend parseUser in parseUsers) // could be many thousands
    {
        if (emails.Where(e => e.EmailAddress == parseUser.Email).ToList().Count > 0)
        {                        
            parseUser.AddContact(contact); // function call

            verifiedUsers.Add(parseUser); // add to my new aggregated list
        }
    }
}

谢谢。

Answer 1

您可以使用可以更有效地搜索的集合，而不是对emails集合中的每个项目进行线性搜索，例如：parseUsersHashSet

foreach (Contact contact in Contacts) // phone contacts, around 500-1000
{
    HashSet<string> emails = new HashSet<string>(
        contact.EmailAddresses.Select(e => e.EmailAddress));

    foreach (Friend parseUser in parseUsers) // could be many thousands
    {
        if(emails.Contains(parseUser.Email))
        {
            parseUser.AddContact(contact); // function call

            verifiedUsers.Add(parseUser); // add to my new aggregated list
        }
    }
}

Answer 2

没有提高很多性能，但提高了可读性：

foreach (Friend parseUser in parseUsers) // could be many thousands
{
    var filterContacts = Contacts.Where(contact =>
                              contact.EmailAddresses.Contains(parseUser.Email));
    if (filterContact.Any())
    {
        parseUser.AddContacts(filterContacts);
        verifiedUsers.Add(parseUser);
    }
}