Sort a Nested string list in C#

Question

What I want to achieve is a alphabetically sorted nested list.

E.g. my input:

fat, twat, gat    //Line 1
cat, hat, bat     // Line 2
twat, lack, rat   // Line 3

I want the output to be:

bat, cat, hat    // Line 2
fat, gat, twat   // Line 1
lack, rat, twat  // Line 3

As you can see, the list is sorted on the inside first, then also on the outside.

My implementation at the moment is using a nested list:

List<List<String>> testSort;

I have managed to sort the inside list using this method:

    public static List<List<String>> sortList(List<List<String>> input)
    {
        input.ForEach(delegate (List<string> o)
        {
            o.Sort();
        });

        return input;
    }

I'm unsure how to sort the list on the outside now. Help would be appreciated!

Thanks in advance!

Answer 1

You can use OrderBy() to sort the outside list based on first element of each list, after each internal list is already sorted:

input.ForEach(t => t.Sort());
input = input.OrderBy(t => t.First()).ToList();

In response to M.kazem Akhgary comment below, I can only think of this solution if you want the sorting of the outer list not only based on the first element but the entire list. Maybe someone else has better solution.

input.ForEach(t => t.Sort());
input.Sort((e1, e2) => {
    for (int i = 0; i < e1.Count; i++)
    {
        if(e1[i] != e2[i])
        {
            return e1[i].CompareTo(e2[i]);
        }
    }

    return 0;
});

Answer 2

Since the signature of sortList has a return type it is best not to modify the contents of the input list - that could just lead to side effects and buggy code.

Here's how I would tackle this:

public static List<List<String>> sortList(List<List<String>> input)
{
    return input
        .Select(x => x.OrderBy(y => y).ToList())
        .OrderBy(x => String.Join(", ", x))
        .ToList();
}

So, given this input:

var input = new List<List<string>>()
{
    new List<string>() { "fat", "twat", "gat", },
    new List<string>() { "cat", "hat", "bat", },
    new List<string>() { "twat", "lack", "rat", },
};

This would be the output: