Format Number like StackoverFlow (rounded to thousands with K suffix)

Question

How to format numbers like SO with C# ?

10, 5k ...

Thanks.

Answer 1

Something like this:

string formatted;
if (num >= 1000) {
    formatted = ((double)num / 1000.0).ToString("N1") + "k";
} else {
    formatted = num.ToString("N0");
}

Answer 2

If the number is bigger than some threshold, divide it by 1000 and then format it to however many decimal places you need.

int input = 12392; // for example

if (input >= 10000)
{
    double thousands = input/1000.0;
    Console.WriteLine(string.Format("{0}K", thousands));
}

Answer 3

Like this: (EDIT: Tested)

static string FormatNumber(int num) {
    if (num >= 100000)
        return FormatNumber(num / 1000) + "K";
    if (num >= 10000) {
        return (num / 1000D).ToString("0.#") + "K";
    }
    return num.ToString("#,0");
}

Examples:

• 1 => 1
• 23 => 23
• 136 => 136
• 6968 => 6,968
• 23067 => 23.1K
• 133031 => 133K

Note that this will give strange values for numbers >= 10⁸.
For example, 12345678 becomes 12.3KK.

Answer 4

You can crate a CustomFormater like this:

public class KiloFormatter: ICustomFormatter, IFormatProvider
{
    public object GetFormat(Type formatType)
    {
        return (formatType == typeof(ICustomFormatter)) ? this : null;
    }

    public string Format(string format, object arg, IFormatProvider formatProvider)
    {
        if (format == null || !format.Trim().StartsWith("K")) {
            if (arg is IFormattable) {
                return ((IFormattable)arg).ToString(format, formatProvider);
            }
            return arg.ToString();
        }

        decimal value = Convert.ToDecimal(arg);

        //  Here's is where you format your number

        if (value > 1000) {
            return (value / 1000).ToString() + "k";
        }

        return value.ToString();
    }
}

And use it like this:

String.Format(new KiloFormatter(), "{0:K}", 15600);

edit: Renamed CurrencyFormatter to KiloFormatter

Answer 5

The code below is tested up to int.MaxValue This is not the most beautiful code but is most efficient. But you can use it as:

123.KiloFormat(); 4332.KiloFormat(); 2332124.KiloFormat(); int.MaxValue.KiloFormat(); (int1 - int2 * int3).KiloFormat();

etc...

public static class Extensions
{
    public static string KiloFormat(this int num)
    {
        if (num >= 100000000)
            return (num / 1000000).ToString("#,0M");

        if (num >= 10000000)
            return (num / 1000000).ToString("0.#") + "M";

        if (num >= 100000)
            return (num / 1000).ToString("#,0K");

        if (num >= 10000)
            return (num / 1000).ToString("0.#") + "K";

        return num.ToString("#,0");
    } 
}

Answer 6

I just wrote some to provide complete information

public static class SIPrefix
{
    private static List<SIPrefixInfo> _SIPrefixInfoList = new
        List<SIPrefixInfo>();

    static SIPrefix()
    {
        _SIPrefixInfoList = new List<SIPrefixInfo>();
        LoadSIPrefix();
    }

    public static List<SIPrefixInfo> SIPrefixInfoList
    { 
        get 
        { 
            SIPrefixInfo[] siPrefixInfoList = new SIPrefixInfo[6];
            _SIPrefixInfoList.CopyTo(siPrefixInfoList);
            return siPrefixInfoList.ToList();
        }
    }

    private static void LoadSIPrefix()
    {
        _SIPrefixInfoList.AddRange(new SIPrefixInfo[]{
            new SIPrefixInfo() {Symbol = "Y", Prefix = "yotta", Example = 1000000000000000000000000.00M, ZeroLength = 24, ShortScaleName = "Septillion", LongScaleName = "Quadrillion"},
            new SIPrefixInfo() {Symbol = "Z", Prefix = "zetta", Example = 1000000000000000000000M, ZeroLength = 21, ShortScaleName = "Sextillion", LongScaleName = "Trilliard"},
            new SIPrefixInfo() {Symbol = "E", Prefix = "exa", Example = 1000000000000000000M, ZeroLength = 18, ShortScaleName = "Quintillion", LongScaleName = "Trillion"},
            new SIPrefixInfo() {Symbol = "P", Prefix = "peta", Example = 1000000000000000M, ZeroLength = 15, ShortScaleName = "Quadrillion", LongScaleName = "Billiard"},
            new SIPrefixInfo() {Symbol = "T", Prefix = "tera", Example = 1000000000000M, ZeroLength = 12, ShortScaleName = "Trillion", LongScaleName = "Billion"},
            new SIPrefixInfo() {Symbol = "G", Prefix = "giga", Example = 1000000000M, ZeroLength = 9, ShortScaleName = "Billion", LongScaleName = "Milliard"},
            new SIPrefixInfo() {Symbol = "M", Prefix = "mega", Example = 1000000M, ZeroLength = 6, ShortScaleName = "Million", LongScaleName = "Million"},
            new SIPrefixInfo() {Symbol = "K", Prefix = "kilo", Example = 1000M, ZeroLength = 3, ShortScaleName = "Thousand", LongScaleName = "Thousand"},
            new SIPrefixInfo() {Symbol = "h", Prefix = "hecto", Example = 100M, ZeroLength = 2, ShortScaleName = "Hundred", LongScaleName = "Hundred"},
            new SIPrefixInfo() {Symbol = "da", Prefix = "deca", Example = 10M, ZeroLength = 1, ShortScaleName = "Ten", LongScaleName = "Ten"},
            new SIPrefixInfo() {Symbol = "", Prefix = "", Example = 1M, ZeroLength = 0, ShortScaleName = "One", LongScaleName = "One"},
        });
    }

    public static SIPrefixInfo GetInfo(long amount, int decimals)
    {
        return GetInfo(Convert.ToDecimal(amount), decimals);
    }

    public static SIPrefixInfo GetInfo(decimal amount, int decimals)
    {
        SIPrefixInfo siPrefixInfo = null;
        decimal amountToTest = Math.Abs(amount);

        var amountLength = amountToTest.ToString("0").Length;
        if(amountLength < 3)
        {
            siPrefixInfo = _SIPrefixInfoList.Find(i => i.ZeroLength == amountLength).Clone() as SIPrefixInfo;
            siPrefixInfo.AmountWithPrefix =  Math.Round(amount, decimals).ToString();

            return siPrefixInfo;
        }

        siPrefixInfo = _SIPrefixInfoList.Find(i => amountToTest > i.Example).Clone() as SIPrefixInfo;

        siPrefixInfo.AmountWithPrefix = Math.Round(
            amountToTest / Convert.ToDecimal(siPrefixInfo.Example), decimals).ToString()
                                        + siPrefixInfo.Symbol;

        return siPrefixInfo;
    }
}

public class SIPrefixInfo : ICloneable
{
    public string Symbol { get; set; }
    public decimal Example { get; set; }
    public string Prefix { get; set; }
    public int ZeroLength { get; set; }
    public string ShortScaleName { get; set; }
    public string LongScaleName { get; set; }
    public string AmountWithPrefix { get; set; }

    public object Clone()
    {
        return new SIPrefixInfo()
                            {
                                Example = this.Example,
                                LongScaleName = this.LongScaleName,
                                ShortScaleName = this.ShortScaleName,
                                Symbol = this.Symbol,
                                Prefix = this.Prefix,
                                ZeroLength = this.ZeroLength
                            };

    }
}

Use:

var amountInfo = SIPrefix.GetInfo(10250, 2);
var amountInfo2 = SIPrefix.GetInfo(2500000, 0);

amountInfo.AmountWithPrefix // 10.25K
amountInfo2.AmountWithPrefix // 2M