在结构golang中按一个字符串组织一个字符串映射

Question

I have a structure of notifications, which looks like:

type Notification struct {
    ID          bson.ObjectId  //unique id for this notification
    ClientID    bson.ObjectId //this identifies the client attached to
    Description string   //notification message
    Date        string   //date using time.Now()
}

So in practice, I have a jumbled collection of data, for example: "User1 has been invited", "User3 has accepted their invite", "User2 has made a payment", "User3 has made a payment", "User1 has accepted their invite", etc, etc...

QUESTION: I don't know how many clients I may have at one time, but I want to be able to search the struct and find out how many unique ClientID's I have. My objective is to start creating a dynamic map where I'm attaching all of the notifications to their individual clients.

The final goal is to be able to pass to the front end (GoLang Template) a display report that looks like this?

ClientID(User1): "User1 has been invited", "User1 has accepted their invite"

ClientID(User2): "User2 has made a payment"

ClientID(User3): "User3 has accepted their invite", "User3 has made a payment"