Linq选择ID为字母数字的最高ID

Question

I have a list of ID where the ID's start with MB (for members) or NM (for non members).

The ID would be like MB-101 or NM-108 etc...

I am trying to select the Highest ID starting with MB and then Add 1 and then save back to DB. Saving is easy but I am not sure how to query the highest Member or Nonmember ID and add one to it. Any help is much appreciated

Answer 1

You can do something like this:

List<string> list = new List<string>() { "MB-101", "MB-102", "MB-103", "MB-104"};
var ids = list.Select(x =>Convert.ToInt32(x.Replace("MB-", "")));//convert all the number parts to integer
list[list.FindIndex(x => x == "MB-" + ids.Max().ToString())] = "MB-" + (ids.Max() + 1);//set the max number after adding one.

You can do the same with your Nonmember ID. It is tested code, it successfully addresses your problem.

Hope it helps.

Answer 2

You can get the max id by splitting your list like below:

var ids = yourList.Where(x => x.ID.StartsWith("MB-")).Select(x => new { ID = x.ID.Split('-')[1] }).ToList();
var maxIdValue = ids.Select(x => int.Parse(x.ID)).ToList().Max();

If you want max id from both starting with MB- and NB- than you can remove above where condition. By this it will fetch max id from both MB- and NB-. Following will be query than:

var ids = yourList.Select(x => new { ID = x.ID.Split('-')[1] }).ToList();
var maxIdValue = ids.Select(x => int.Parse(x.ID)).ToList().Max();

Answer 3

you can try like this

List<string> lststr = new List<string>() { "MB-101", "MB-103", "MB-102", "NM-108" };

var result = "MB-"+ lststr
            .Where(x=>x.Contains("MB"))
            .Select(x => Regex.Replace(x, @"[^\d]", ""))
            .OrderByDescending(x=>x)
            .FirstOrDefault();

it will return MB-103 because it will first check if the string contains MB then it will replace everything with "" other than digit and OrderByDescending it will order by Descending so that the highest value will be on top and at last FirstOrDefault will get the fist value

Answer 4

You have to do OrderByDescending your list by replacing MB or NM with empty and get FirstOrDefault from ordered list. Please check below example.

CODE:

List<string> list = new List<string>() { "MB-101", "MB-102", "MB-109", "MB-105", "NM-110"};
var maxMember = list.OrderByDescending(m=>Convert.ToInt16(m.Replace("MB-","").Replace("NM-",""))).ToList().FirstOrDefault();
Console.WriteLine(maxMember.ToString());