What's the name of a table of values/frequencies?

I have a main data store which has a big set of perfectly ordinary records, which might look like (all examples here are pseudocode):

class Person {
    string FirstName;
    string LastName;
    int Height;
    // and so on...
}

I have a supplementary data structure I'm using for answering statistical questions efficiently. It's computed from the main data store, and it's a dictionary that looks like:

// { (field_n开发者_高级运维ame, field_value) => count }
Dictionary<Tuple<string, object>, int>;

For example, one entry of the dictionary might be:

(LastName, "Smith") => 345

which means in 345 of the Person records, the LastName field is "Smith" (or was, at the time this dictionary was last computed).

What is this supplementary dictionary called? I think it'd be easier to talk about if it had a proper name.

I might call it a "histogram", if I was to print the entire thing graphically (but it's just a data structure, not a visual representation). If I stored the locations of these values (instead of just their count) I might call it an "inverted index".

I think you have found the most appropriate name already: frequency table or frequency distribution.