Sorting a generic list by an external sort order

Question

I have a generic list

Simplified example

var list = new List<string>()
  {
    "lorem1.doc",
    "lorem2.docx",
    "lorem3.ppt",
    "lorem4.pptx",
    "lorem5.doc",
    "lorem6.doc",
  };

What I would like to do is to sort these items based on an external list ordering

In example

var sortList = new[] { "pptx", "ppt", "docx", "doc" };

// Or
var sortList = new List<string>() { "pptx", "ppt", "docx", "doc" };

Is there anything built-in to linq that could help me achieve this or do I have to go the foreach way?

Answer 1

With the list you can use IndexOf for Enumerable.OrderBy:

var sorted = list.OrderBy(s => sortList.IndexOf(Path.GetExtension(s)));

So the index of the extension in the sortList determines the priority in the other list. Unknown extensions have highest priority since their index is -1.

But you need to add a dot to the extension to get it working:

var sortList = new List<string>() { ".pptx", ".ppt", ".docx", ".doc" };

If that's not an option you have to fiddle around with Substring or Remove, for example:

var sorted = list.OrderBy(s => sortList.IndexOf(Path.GetExtension(s).Remove(0,1)));

Answer 2

This solution will work even if some file names do not have extensions:

var sortList = new List<string>() { "pptx", "ppt", "docx", "doc" };
var list = new List<string>()
  {
    "lorem1.doc",
    "lorem2.docx",
    "lorem3.ppt",
    "lorem4.pptx",
    "lorem5.doc",
    "lorem6.doc",
  };

var result = 
       list.OrderBy(f => sortList.IndexOf(Path.GetExtension(f).Replace(".","")));

Answer 3

You could try using Array.IndexOf() method:

var sortedList = list.OrderBy(i => sortList.IndexOf(System.IO.Path.GetExtension(i))).ToList();