Question

I have over a thousand folders, each folder contains one or more files with the following names:

Unordered:

Alison.ext
Heather.ext
Molly.ext
Paula.ext
Sam.ext

Ordered:

Molly.ext
Sam.ext
Heather.ext
Alison.ext
Paula.ext

I would like to write an expression to sort this list as described above.

Answer 1

//Creating a dictionary with the custom order
var order = "MSHAP";
var orderDict = order.Select((c,i)=>new {Letter=c, Order=i})
                     .ToDictionary(o => o.Letter, o => o.Order);

var list = new List<string>{"A.ext", "H.ext", "M.ext", "P.ext", "S.ext"};

//Ordering by the custom criteria
var result = list.OrderBy(item => orderDict[item[0]]);

Instead of calling orderDict[item[0]] you could have a nice helper method that cares for the fringe cases (non existent letters, null, and so on). But that’s the idea.