How do I sort numbers written in string format("one "two" three" etc.) according to their value using LINQ C# lambda expressions

Question

public static IEnumerable<string> OrderingReversal()
{
    string[] digits = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };

    var res = digits.Where(w => w[1] == 'i')
                    .OrderByDescending(w => Convert.ToInt32(w)).ToList<string>();

    return res;
}

I would like the output to be: "nine", "eight", "six" and "five" I tried to achieve this by the code I provided above. However, I am receiving runtime error: System.FormatException: 'Input string was not in a correct format.'

Any Help would be appreciated. Thank you!

The error is with the covert.ToInt32, "two" != "2". You'll need to assign a numeric value to each string. Check out https://www.tutorialspoint.com/keyvaluepair-in-chash as an example. — gman, Mar 01 '22 at 17:58
`Select` has a helpful overload that includes the index which allows you to do this in one fell swoop: `digits.Select((word, value) => new { word, value }).Where(p => p.word.Contains("i")).OrderByDescending(p => p.value).Select(p => p.word)`. Do analyze the individual components to see how this works. — Jeroen Mostert, Mar 01 '22 at 18:04
Thank you Jeroen and everyone else who commented. For some reason i did not catch the fact that index == values. How do I mark it as solved? — Anonymous Future Developer, Mar 01 '22 at 18:12
Your digits are sorted already. Why do you want to sort them? Just loop in reverse order and pick the ones with `"i"`. `for (int i = digits.Length - 1; i >= 0; i--) { if (digits[i][1] == "i") { yield return digits[i]; } }`. The [yield return](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/yield) produces the `IEnumerable`. — Olivier Jacot-Descombes, Mar 01 '22 at 18:16
Thank You Mr. Olivier. The exercise requested the use of OrderBy LINQ function. I have been stuck on it for few hours and finally decided to post it here after I gave up to solve it myself. Mr. Jeroen's solution completely solved my problem. Thank you very much again! — Anonymous Future Developer, Mar 01 '22 at 18:22

Scott Hannen · Accepted Answer · 2022-03-01T18:19:56.647

A big part of the solution is found in other answers like this one but more is needed to sort the results.

Here's a class that will take a list of strings and return them sorted by the numeric values they represent:

public delegate long ConvertStringToNumberDelegate(string number);

public class NumbersAsTextSorter
{
    private readonly ConvertStringToNumberDelegate _convertStringToNumberFunction;

    public NumbersAsTextSorter(ConvertStringToNumberDelegate convertStringToNumberFunction)
    {
        _convertStringToNumberFunction = convertStringToNumberFunction;
    }

    public IEnumerable<string> ReverseSort(IEnumerable<string> input)
    {
        var textWithNumbers = input.Select(i => new {input = i, value = _convertStringToNumberFunction(i)});

        return textWithNumbers.OrderByDescending(t => t.value).Select(s => s.input);
    }
}

This will create a collection of text inputs matched with numeric values. It sorts the collection by the numeric value and then returns the text inputs in that sorted order.

As you can see, a critical detail is missing. How do you convert "one" to 1, "two" to 2, and so forth?

For that you need an implementation of the delegate - ConvertStringToNumberDelegate. You can get that by using the class in the the answer I referenced above.

For convenience I've copied that static method (for which I am explicitly not taking credit!) into a static class:

public static class TestToNumbers
{
    private static Dictionary<string, long> numberTable =
        new Dictionary<string, long>
        {{"zero",0},{"one",1},{"two",2},{"three",3},{"four",4},
        {"five",5},{"six",6},{"seven",7},{"eight",8},{"nine",9},
        {"ten",10},{"eleven",11},{"twelve",12},{"thirteen",13},
        {"fourteen",14},{"fifteen",15},{"sixteen",16},
        {"seventeen",17},{"eighteen",18},{"nineteen",19},{"twenty",20},
        {"thirty",30},{"forty",40},{"fifty",50},{"sixty",60},
        {"seventy",70},{"eighty",80},{"ninety",90},{"hundred",100},
        {"thousand",1000},{"million",1000000},{"billion",1000000000},
        {"trillion",1000000000000},{"quadrillion",1000000000000000},
        {"quintillion",1000000000000000000}};
    public static long ToLong(string numberString)
    {
        var numbers = Regex.Matches(numberString, @"\w+").Cast<Match>()
            .Select(m => m.Value.ToLowerInvariant())
            .Where(v => numberTable.ContainsKey(v))
            .Select(v => numberTable[v]);
        long acc = 0, total = 0L;
        foreach (var n in numbers)
        {
            if (n >= 1000)
            {
                total += (acc * n);
                acc = 0;
            }
            else if (n >= 100)
            {
                acc *= n;
            }
            else acc += n;
        }
        return (total + acc) * (numberString.StartsWith("minus",
            StringComparison.InvariantCultureIgnoreCase) ? -1 : 1);
    }
}

Now you can create an instance of NumbersAsTextSorter which uses that static method to convert text to numbers. I've done that in this unit test which passes:

[TestMethod]
public void TestSorting()
{
    var sorter = new NumbersAsTextSorter(TestToNumbers.ToLong);
    var output = sorter.ReverseSort(new string[] { "one", "three hundred", "zero" });
    Assert.IsTrue(output.SequenceEqual(new string[] { "three hundred", "one", "zero" }));
}

For clarity, this is passing in "one", "three hundred", and "zero" and asserting that after it's sorted, the sequence is "three hundred", "one", "zero".

Thank you very much Mr. Scott for such a elaborate answer. This was supposed to be beginner level task but I will try to analyze your answer. — Anonymous Future Developer, Mar 01 '22 at 18:16
I missed the detail that the sort was supposed to be in descending order Fixed. — Scott Hannen, Mar 01 '22 at 18:20

score 1 · Answer 2 · answered Mar 01 '22 at 19:43

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] digits = { "Zero", "one", "two", "Three", "four", "five", "Six", "seven", "eight", "nine" };

            var asc = OrderNumberStringsByValue(digits);
            var dec = OrderNumberStringsByValue(digits, true);
            
            string[] myDigits = { "Eight", "nine", "Five", "six" };

            var myAsc = OrderNumberStringsByValue(myDigits);
            var myDec = OrderNumberStringsByValue(myDigits, true);

            Console.WriteLine($"asc:   {string.Join(", ", asc)}");
            Console.WriteLine($"dec:   {string.Join(", ", dec)}");
            Console.WriteLine($"myAsc: {string.Join(", ", myAsc)}");
            Console.WriteLine($"myDec: {string.Join(", ", myDec)}");

            Console.ReadLine();
        }

        public static IEnumerable<string> OrderNumberStringsByValue(IEnumerable<string> numbers, bool decending = false)
        {
            return numbers.OrderBy(n => (decending ? -1 : 1) * (int)Enum.Parse(typeof(Numbers), n.ToLower()));
        }
    }

    enum Numbers : int
    {
        zero = 0,
        one = 1,
        two = 2,
        three = 3,
        four = 4,
        five = 5,
        six = 6,
        seven = 7,
        eight = 8,
        nine = 9
    }
}

How do I sort numbers written in string format("one "two" three" etc.) according to their value using LINQ C# lambda expressions

2 Answers2