复杂的LINQ查询

Question

I know LINQ but my knowledge is pretty much only selects, where, orderby and all of the most common functions. Now I have a need to do something that I think is really difficult and maybe not even possible to do just with LINQ. What I have is a list of people. That's east to query but I need to create a text string from that list. The text string has to give a letter followed by the name of each person.

IList<person> Person

I need to be able to have a LINQ statement that checks through the Person list. I need to be able to look for names that appear more than once. So far I have the following. It works okay but doesn't give everything needed:

Person[0] name="Fred" &
Person[1] name="Pete" &
Person[2] name="Tony" the var abc = "a) Fred. b) Pete. c) Tony 

var a = "";
foreach (var person in _persons
            .Select((data, value) => new { Data = data, Value = value })
        {
            a = a + (char)(details.Value + 64) + details.name
        }

What I need is the additional functionality so that:

Person[0] name="John" then var abc = "a) John."

Person[1] name="John" &
Person[3] name="John" then var abc = "b) & d) John."

Person[1] name="John" &
Person[2] name="John" &
Person[3] name="John" then var abc = "b),c) & d) John."

In other words, get the names and put a character before them that shows what position the name is in the list. However if the name appears twice then instead of a)name1. b)name1 I need to get a),b) name.

It's something I can't really figure out how to do. I would appreciate any advice or pointers that anyone can give me.

Answer 1

I think I understand it, but I deserve a medal if I do.

foreach (var group in _persons
        .Select((data, value) => new { Data = data, Value = value }
        .GroupBy (x => x.Data))
    {
        foreach (var item in group)
            a = a + (char)(item.Value + 64) + ") ";

        a = a + group.Key;
    }

Answer 2

Given:

var persons=new[] {"Fred", "John", "John", "Pete", "John"};

You can write:

        char id = 'a';
        foreach (var row in persons
            .Select(w => new { id = id++, name = w })
            .GroupBy(w => w.name)
            .Select(w => w
                .Select(ww => ww.id + ")")
                .Aggregate((c, n) => c + "&" + n)
                + " " + w.Key))
        {
            Console.WriteLine(row);
        }

And that gives you:

a) Fred
b)&c)&e) John
d) Pete

Answer 3

What you need is to first group by the names, and then convert them to strings.

var result = names
    .Select((name, index) => new { Name = name, Prefix = (char)(index + 'a') + ")" })
    .GroupBy(p => p.Name, p => p.Prefix)
    .Select(g => string.Join(" & ", g) + " " + g.Key);

This example doesn't entirely do the formatting of the a), b) & c) thing (instead it gives a) & b) & c) , but it should get you started.

Answer 4

You can use Count() to achieve this. It can take a function to determine whether something should be counted.