C# filter 基于类属性的类列表字典

Question

I have this dictionary Dictionary<string, List<Payments>> , which holds employees, each employee having a list of payments. The Payments class has a string property named PayCategoryId. I want to filter this dictionary and get only the employees with payments having some specific PayCategoryId values and for each employee only those payments. I'm pretty sure this can be achieved by using LINQ, but I have almost zero experience with LINQ, so need your help.

The original (unfiltered) dictionary has 76 items (employees). The employee which I'll use as an example has 27 payments, some of them having the required PayCategoryId.

What I've done:

1. List with the required PayCategoryId:

    var payCategoriesID = new List<string> (){ "a", "b", "c" };

2. Semi-filter the dictionary with this LINQ (I'm sure it's a mess, but is working!):

    var result = dict.Where(o => o.Value.Where(x => payCategoriesID.Contains(x.PayCategoryId)).Any()).ToDictionary(mc => mc.Key, mc => mc.Value);

3. The semi-filtered resulted dictionary has only 34 items. The employees having no payments with the required PayCategoryId were filtered out. But my example employee still has all 27 payments in the list. I need his list to be filtered too and have only the payments having PayCategoryId = one of the IDs from payCategoriesID list. Of course, the example employee is just an example, all employees should be filtered.

Can you help, please?

Adrian

Answer 1

You can use Select() to project into an enumerable of anonymous type and get only the value you want, then build back a dictionary.

var match = dict
        .Select(kv => new
        {
            Employee = kv.Key,
            Payments = kv.Value.Where(p => payCategoriesID.Contains(p.PayCategoryId))
        })
        .Where(emp => emp.Payments.Any())
        .ToDictionary(k => k.Employee, v => v.Payments);

The first step creates an object with key and filtered values, then the Where() remove the empty lists. That way you only iterate through the ids list once (per element on the dictionary).

---

Also, not really related, but the Any() method has an overload which takes a predicate, so instead of

o.Value.Where(x => payCategoriesID.Contains(x.PayCategoryId)).Any()

you can do directly

o.Value.Any(x => payCategoriesID.Contains(x.PayCategoryId))

Same goes for other LINQ methods such as Count() , First() , FirstOrDefault() , Last() and more.

Answer 2

var result = dict.Where(o => o.Value.Where(x => payCategoriesID.Contains(x.PayCategoryId)).Any()).ToDictionary(mc => mc.Key, mc => mc.Value.Where(t=> payCategoriesID.Contains(t.PayCategoryId)));