select latest date from string array - vb.net

Question

below is the array of strings , ie , the names of the files and folders is something i will get in the array. now from this array i need to select the newest macro file. ie , among all the strings which ends with xslm in the string array , i will select the one which has the string 20200817_W.xslm .which is the latest file kept.
Edit :
for Min.Rep of the prob ,
here we are talking about a string array like below
{IOH Bot Files , Archive , IOH_AllPlants_BI_2020817_W.xlsm, IOH_AllPlants_BI_2020817_W.xlsm ,... }
from this array i need to choose , IOH_AllPlants_BI_2020817_W.xlsm- because this string has a date component in it and it is the latest in the available list of strings

Answer 1

You don't even need LINQ for this one, because of the regularity of the data:
Array.Sort(arr2)
Dim latestOne = arr(arr.Length-1)
Perhaps we should ensure only xlsm files of the right name are considered:
Dim arr2 = Array.FindAll(arr, Function(x) x.StartsWith("IOH_AllPlants_BI_") AndAlso x.EndsWith("xlsm"))
Array.Sort(arr)
Dim latestOne = arr(arr.Length-1)
We could use LINQ, and (keeping our "only matching names" logic) rather than using an expensive sort, just ask for the Max:
Dim onlyIOHXLSMFiles = arr.Where(Function(x) x.StartsWith("IOH_AllPlants_BI_") AndAlso x.EndsWith("xlsm"))
Dim latestOne = arr.Max()
We don't need to parse this date because it's yyyyMMdd; it sorts just fine as a string. Because it's just a simple string property it is fine to use with just Max which is more efficient than the typical "OrderBy/First" approach.
If the list was not just of a simple type, but instead was eg Person and you were wanting the most recently born Person (rather than just their birthdate, which is what Max would give you) you could:
Dim lastOne = personArr.OrderBy(Function(p) p.Birthdate).Last()
I use OrderBy/Last rather then OrderByDescending/First because it's fewer characters to type for the same effect
All these code samples (with the exception of the last one) make use of an array arr created like:
Dim arr = {"IOH Bot Files" , "Archive" , "IOH_AllPlants_BI_2020817_W.xlsm", "IOH_AllPlants_BI_2020817_W.xlsm" , ... }

Answer 2

See sample logic below which returns what you need. You can change the logic according to your need. You should read the file names to an array and use below logic.
using System;
using System.Linq;
namespace SampleConsoleApp
{
class Program
{
static void Main(string[] args)
{
string[] data = new string[] {
"IOH_AllPlants_BI_20200810_W.xslm"
, "IOH_AllPlants_BI_20200803_W.xslm"
, "IOH_AllPlants_BI_20200727_W.xslm"
, "IOH_AllPlants_BI_20200720_W.xslm",
"IOH_AllPlants_BI_20200817_W.xslm"
, "IOH_AllPlants_BI_20200713_W.xslm"
, "IOH_AllPlants_BI_20200706_W.xslm"};
var result = data.Select(s => s.Split('_')).Select(x => x[3]).OrderByDescending(x => x).First();
//result returns 20200817
}
}
}