Can you round a .NET TimeSpan object?

Question

Can you round a .NET TimeSpan object?

I have a Timespan value of: 00:00:00.6193789

Is there a simple way to keep it a TimeSpan object but round it to something like
00:00:00.62?

Mulligrubs

Just a warning to others. I was going down the road of using TimeSpan as a public property off of a business object. Didn't realize that TimeSpan was not a "XmlSerializable" data type. Discussion on the issue: devnewsgroups.net/group/microsoft.public.dotnet.framework/… – Mulligrubs

Answer 1

Sorry, guys, but both the question and the popular answer so far are wrong :-)

The question is wrong because Tyndall asks for a way to round but shows an example of truncation.

Will Dean's answer is wrong because it also addresses truncation rather than rounding. (I suppose one could argue the answer is right for one of the two questions, but let's leave philosophy aside for the moment...)

Here is a simple technique for rounding:

int precision = 2; // Specify how many digits past the decimal point
TimeSpan t1 = new TimeSpan(19365678); // sample input value

const int TIMESPAN_SIZE = 7; // it always has seven digits
// convert the digitsToShow into a rounding/truncating mask
int factor = (int)Math.Pow(10,(TIMESPAN_SIZE - precision));

Console.WriteLine("Input: " + t1);
TimeSpan truncatedTimeSpan = new TimeSpan(t1.Ticks - (t1.Ticks % factor));
Console.WriteLine("Truncated: " + truncatedTimeSpan);
TimeSpan roundedTimeSpan =
    new TimeSpan(((long)Math.Round((1.0*t1.Ticks/factor))*factor));
Console.WriteLine("Rounded: " + roundedTimeSpan);

With the input value and number of digits in the sample code, this is the output:

Input: 00:00:01.9365678
Truncated: 00:00:01.9300000
Rounded: 00:00:01.9400000

Change the precision from 2 digits to 5 digits and get this instead:

Input: 00:00:01.9365678
Truncated: 00:00:01.9365600
Rounded: 00:00:01.9365700

And even change it to 0 to get this result:

Input: 00:00:01.9365678
Truncated: 00:00:01
Rounded: 00:00:02

Finally, if you want just a bit more control over the output, add some formatting. Here is one example, showing that you can separate the precision from the number of displayed digits. The precision is again set to 2 but 3 digits are displayed, as specified in the last argument of the formatting control string:

Console.WriteLine("Rounded/formatted: " + 
  string.Format("{0:00}:{1:00}:{2:00}.{3:000}",
      roundedTimeSpan.Hours, roundedTimeSpan.Minutes,
      roundedTimeSpan.Seconds, roundedTimeSpan.Milliseconds));
// Input: 00:00:01.9365678
// Truncated: 00:00:01.9300000
// Rounded: 00:00:01.9400000
// Rounded/formatted: 00:00:01.940

---

2010.01.06 UPDATE: An Out-of-the-box Solution

The above material is useful if you are looking for ideas; I have since had time to implement a packaged solution for those looking for ready-to-use code.

Note that this is uncommented code. The fully commented version with XML-doc-comments will be available in my open source library by the end of the quarter. Though I hesitated to post it "raw" like this, I figure that it could still be of some benefit to interested readers.

This code improves upon my code above which, though it rounded, still showed 7 places, padded with zeroes. This finished version rounds and trims to the specified number of digits.

Here is a sample invocation:

Console.Write(new RoundedTimeSpan(19365678, 2).ToString());
// Result = 00:00:01.94

And here is the complete RoundedTimeSpan.cs file:

using System;

namespace CleanCode.Data
{
    public struct RoundedTimeSpan
    {

        private const int TIMESPAN_SIZE = 7; // it always has seven digits

        private TimeSpan roundedTimeSpan;
        private int precision;

        public RoundedTimeSpan(long ticks, int precision)
        {
            if (precision < 0) { throw new ArgumentException("precision must be non-negative"); }
            this.precision = precision;
            int factor = (int)System.Math.Pow(10, (TIMESPAN_SIZE - precision));

            // This is only valid for rounding milliseconds-will *not* work on secs/mins/hrs!
            roundedTimeSpan = new TimeSpan(((long)System.Math.Round((1.0 * ticks / factor)) * factor));
        }

        public TimeSpan TimeSpan { get { return roundedTimeSpan; } }

        public override string ToString()
        {
            return ToString(precision);
        }

        public string ToString(int length)
        { // this method revised 2010.01.31
            int digitsToStrip = TIMESPAN_SIZE - length;
            string s = roundedTimeSpan.ToString();
            if (!s.Contains(".") && length == 0) { return s; }
            if (!s.Contains(".")) { s += "." + new string('0', TIMESPAN_SIZE); }
            int subLength = s.Length - digitsToStrip;
            return subLength < 0 ? "" : subLength > s.Length ? s : s.Substring(0, subLength);
        }
    }
}

---

2010.02.01 UPDATE: Packaged solution now available

I just released a new version of my open-source libraries yesterday, sooner than anticipated, including the RoundedTimeSpan I described above. Code is here; for the API start here then navigate to RoundedTimeSpan under the CleanCode.Data namespace. The CleanCode.DLL library includes the code shown above but provides it in a finished package. Note that I have made a slight improvement in the ToString(int) method above since I posted it on 2010.01.06.

Basilicata

This is overkill. Looking over the other answers, none of them is as simple as it can be. See my answer – Epistrophe

NetMage's newer answer is also nice, if you want multiples of an arbitrary timespan. E.g. sometimes you want seconds, sometimes minutes, sometimes milliseconds. – Epistrophe

For anyone like me looking at this question in 2024 and getting hella confused why answers like this are saying the question shows an example of truncation - the original question did show an example of truncation but has since been edited (correctly) to show an example of rounding. – Percival

Thanks for posting that update @Percival ! – Basilicata

Answer 2

Simplest one-liner if you are rounding to whole seconds:

public static TimeSpan RoundSeconds( TimeSpan span ) {
    return TimeSpan.FromSeconds( Math.Round( span.TotalSeconds ) );
}

---

To round to up to 3 digits (e.g. tenths, hundredths of second, or milliseconds:

public static TimeSpan RoundSeconds( TimeSpan span, int nDigits ) {
    // TimeSpan.FromSeconds rounds to nearest millisecond, so nDigits should be 3 or less - won't get good answer beyond 3 digits.
    Debug.Assert( nDigits <= 3 );
    return TimeSpan.FromSeconds( Math.Round( span.TotalSeconds, nDigits ) );
}

---

For more than 3 digits, its slightly more complex - but still a one-liner. This can also be used for 3 or less digits - it is a replacement for the version shown above:

public static TimeSpan RoundSeconds( TimeSpan span, int nDigits ) {
    return TimeSpan.FromTicks( (long)( Math.Round( span.TotalSeconds, nDigits ) * TimeSpan.TicksPerSecond) );
}

If you want a string (according to a comment, this technique only works up to 7 digits):

public static string RoundSecondsAsString( TimeSpan span, int nDigits ) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < nDigits; i++)
        sb.Append( "f" );
    return span.ToString( @"hh\:mm\:ss\." + sb );
}

---

For time of day, as hours and minutes, rounded:

public static TimeSpan RoundMinutes(TimeSpan span)
    {
        return TimeSpan.FromMinutes(Math.Round(span.TotalMinutes));
    }

If you have a DateTime, and want to extract time of day rounded:

DateTime dt = DateTime.Now();
TimeSpan hhmm = RoundMinutes(dt.TimeOfDay);

To display rounded 24 hour time:

string hhmmStr = RoundMinutes(dt.TimeOfDay).ToString(@"hh\:mm");

To display time of day in current culture:

string hhmmStr = new DateTime().Add(RoundMinutes(dt.TimeOfDay)).ToShortTimeString();

---

Credits:

cc1960's answer shows use of FromSeconds, but he rounded to whole seconds. My answer generalizes to specified number of digits.

Ed's answer suggests using a format string, and includes a link to the formatting document.

Chris Marisic shows how to apply ToShortTimeString to a TimeSpan (by first converting to a DateTime).

---

To round to multiple of some other unit, such as 1/30 second:

    // Rounds span to multiple of "unitInSeconds".
    // NOTE: This will be close to the requested multiple,
    // but is not exact when unit cannot be exactly represented by a double.
    // e.g. "unitInSeconds = 1/30" isn't EXACTLY 1/30,
    // so the returned value won't be exactly a multiple of 1/30.
    public static double RoundMultipleAsSeconds( TimeSpan span, double unitInSeconds )
    {
        return unitInSeconds * Math.Round( span.TotalSeconds / unitInSeconds );
    }

    public static TimeSpan RoundMultipleAsTimeSpan( TimeSpan span, double unitInSeconds )
    {
        return TimeSpan.FromTicks( (long)(RoundMultipleAsSeconds( span, unitInSeconds ) * TimeSpan.TicksPerSecond) );

        // IF USE THIS: TimeSpan.FromSeconds rounds the result to nearest millisecond.
        //return TimeSpan.FromSeconds( RoundMultipleAsSeconds( span, unitInSeconds ) );
    }

    // Rounds "span / n".
    // NOTE: This version might be a hair closer in some cases,
    // but probably not enough to matter, and can only represent units that are "1 / N" seconds.
    public static double RoundOneOverNAsSeconds( TimeSpan span, double n )
    {
        return Math.Round( span.TotalSeconds * n ) / n;
    }

    public static TimeSpan RoundOneOverNAsTimeSpan( TimeSpan span, double n )
    {
        return TimeSpan.FromTicks( (long)(RoundOneOverNAsSeconds( span, n ) * TimeSpan.TicksPerSecond) );

        // IF USE THIS: TimeSpan.FromSeconds rounds the result to nearest millisecond.
        //return TimeSpan.FromSeconds( RoundOneOverNAsSeconds( span, n ) );
    }

To use one of these to round to multiples of 1/30 second:

    private void Test()
    {
        long ticks = (long) (987.654321 * TimeSpan.TicksPerSecond);
        TimeSpan span = TimeSpan.FromTicks( ticks );
        TestRound( span, 30 );
        TestRound( TimeSpan.FromSeconds( 987 ), 30 );
    }

    private static void TestRound(TimeSpan span, int n)
    {
        var answer1 = RoundMultipleAsSeconds( span, 1.0 / n );
        var answer2 = RoundMultipleAsTimeSpan( span, 1.0 / n );
        var answer3 = RoundOneOverNAsSeconds( span, n );
        var answer4 = RoundOneOverNAsTimeSpan( span, n );
    }

Results viewed in debugger:

// for 987.654321 seconds:
    answer1 987.66666666666663  double
    answer2 {00:16:27.6666666}  System.TimeSpan
    answer3 987.66666666666663  double
    answer4 {00:16:27.6666666}  System.TimeSpan

// for 987 seconds:
    answer1 987 double
    answer2 {00:16:27}  System.TimeSpan
    answer3 987 double
    answer4 {00:16:27}  System.TimeSpan

Epistrophe

I like this, but I also like extension methods: public static TimeSpan RoundSeconds(this TimeSpan span, int nDigits = 0) – Ange

NetMage's newer answer is nice, if you want multiples of an arbitrary timespan. E.g. sometimes you want seconds, sometimes minutes, sometimes milliseconds. – Epistrophe

For RoundSecondsAsString: Mind that the maximum number of digits (f's) that you can append is 7! Also there will be an orphaned decimal point at the end if nDigits == 0 – Froehlich

This is cool; I'd missed the fact that the TimeSpan.Total{Units} properties include the non-integral portion, even though it makes perfect sense. (I had been thinking it was more like a DateTime's Day or Minute property.) – Criollo

Answer 3

TimeSpan is little more than a wrapper around the 'Ticks' member. It's pretty easy to create a new TimeSpan from a rounded version of another TimeSpan's Ticks.

TimeSpan t1 = new TimeSpan(2345678);
Console.WriteLine(t1);
TimeSpan t2 = new TimeSpan(t1.Ticks - (t1.Ticks % 100000));
Console.WriteLine(t2);

Gives:

00:00:00.2345678
00:00:00.2300000

Breakaway

The answer truncates (and to be fair, so did the question). If you instead want to round, some of the other answers do so, but none is as simple as it can be. See my answer. – Epistrophe

NetMage's newer answer is also nice, if you want multiples of an arbitrary timespan. E.g. sometimes you want seconds, sometimes minutes, sometimes milliseconds. – Epistrophe

Answer 4

Given some of the comments about rounding to seconds, I thought rounding to any TimeSpan would be nice:

public static TimeSpan Round(this TimeSpan ts, TimeSpan rnd) {
    if (rnd == TimeSpan.Zero)
        return ts;
    else {
        var rndTicks = rnd.Ticks;
        var ansTicks = ts.Ticks + Math.Sign(ts.Ticks) * rndTicks / 2;
        return TimeSpan.FromTicks(ansTicks - ansTicks % rndTicks);
    }
}
public static TimeSpan Round(this TimeSpan ts) => ts.Round(TimeSpan.FromSeconds(1));

Given the potential inaccuracies rounding to ticks when dealing with fractional units (per @ToolmakerSteve), I am adding a fractional rounding option for when you need higher accuracy and are rounded to a computer fractional seconds:

public static TimeSpan RoundToFraction(this TimeSpan ts, long num, long den) => (den == 0.0) ? TimeSpan.Zero : TimeSpan.FromTicks((long)Math.Round(Math.Round((double)ts.Ticks * (double)den / num / TimeSpan.TicksPerSecond) * (double)num / den * TimeSpan.TicksPerSecond));
public static TimeSpan RoundToFraction(this TimeSpan ts, long den) => (den == 0.0) ? TimeSpan.Zero : TimeSpan.FromTicks((long)(Math.Round((double)ts.Ticks * den / TimeSpan.TicksPerSecond) / den * TimeSpan.TicksPerSecond));

Ange

I like this (so upvoted). And it will work correctly for the vast majority of situations people will use. FWIW, Be aware of a minor limitation: Only correct if the desired "rnd" (divisor) is expressible as a whole number of ticks. For example, if one wanted to round a large number of ticks to nearest 30th of a second, don't ask me why :D, this would not be helpful. Fortunately, all the common cases work fine - IF one second is a power-of-10 of ticks (e.g. 100,000 ticks = 1 second), then 1/10th second, 1/100th second etc work, as well as 2/10th second, 2/100th, .., and 5/10th second, ... – Epistrophe

Good point, but that is no different than most other floating point operations in programming. OTOH, it is difficult to create 1/30 of a second TimeSpan since Microsoft didn't implement FromTotal* variations of the factory functions so hopefully you need to know what you're doing to get there. – Ange

On the contrary, it is different in the following way: your solution introduces a limitation that does not exist in the underlying data. You introduced this limitation by using a divisor, "rnd" that is an integer number of ticks. The result may be noticeably wrong if someone wants a divisor that is not exactly expressible as an integer number of ticks. This is a larger error than floating point round off error, which would at most result in an answer that was off by 1. Anyone using this needs to understand this limitation. – Epistrophe

.. in practice, it looks like it only matters for tiny values of rnd. So 1/30 of a second the error is not enough to matter for almost any use. The smaller rnd gets, the more it may become an issue. I just wanted to flag the fact that there is a potential inaccuracy here, which happens because TimeSpan is not a floating point value, so becomes more inaccurate as values get smaller. (The solution in those cases would be to not attempt to represent rnd as a TimeSpan; instead use a floating-point number of seconds.) – Epistrophe

.. or even better, pass in the number you want to divide by. I mean, if you want a result in 30ths of a second, take "30" as the second parameter, instead of "1/30". [Again, let me stress that I did upvote the answer as-is; I am making minor comments that won't matter for most people looking for a solution. This is a very useful answer.] – Epistrophe

Since the smallest unit of time expressible in a TimeSpan is one tick, doesn't that mean you can't round a TimeSpan evenly to 1/30 of a second, no matter how you do the math? – Ange

I haven't made it clear what the problem is. Your approach gives a noticeably wrong answer for units of 1/30 second, for some input values. More so as the inputs get larger. This is different than rounding, which would give an answer that is as close as possible. The difference could be seen by running my answer and your answer, for a bunch of different random inputs, and seeing where they differ, and by how much. [The differences will usually be small, and often non-existent, but they are there. This isn't the correct math.] – Epistrophe

@Epistrophe What answer of yours can I use to round to 1/30 second? – Ange

@Epistrophe I think I see part of the problem is that TimeSpan.FromSeconds is specified as only being accurate to the millisecond (!). – Ange

sorry, I forgot that the answer I posted here only works with digits, so 1/10, 1/100 etc. I've add an example for rounding to specified fraction of a second. As you mentioned, the result can't be EXACTLY 1/30 second multiple in many cases, since PC float or double values don't exactly represent 1/30 second - but it will be as close as possible, especially method "RoundOneOverN". – Epistrophe

@Epistrophe I would suggest not using FromSeconds - it is only accurate to the millisecond. I wrote my own that converts to ticks and then to TimeSpan. – Ange

Yes, I just discovered that myself. See corrected answer. – Epistrophe

After further examination: because you use FromTicks instead of FromSeconds, your answer probably works fine, except when "ts" is VERY large, it is possible that the miniscule unavoidable inaccuracy in "rndTicks" gets magnified by "ansTicks % rndticks" - that's why I don't recommend converting "rnd" to ticks before performing the rounding. OTOH the tiny possible inaccuracy is not worth worrying about - and can only happen at all when "ts" is VERY large. – Epistrophe

@Epistrophe Some tests I have run with 1/30th rounding with 0-30 seconds shows what seem to be problems (to me), but are perhaps just limitations of rounding to ticks. – Ange

@Epistrophe I added some fractional rounding functions somewhat like yours, still based on FromTicks. – Ange

Doesn't work for negative timespans. I wanted to use this to round to the nearest number of days, but I found that TimeSpan.FromDays(-4).Round(TimeSpan.FromDays(1)) results in -3 days. – Criollo

@Gyromite Updated to handle negative TimeSpans. – Ange

Answer 5

new TimeSpan(tmspan.Hours, tmspan.Minutes, tmspan.Seconds, (int)Math.Round(Convert.ToDouble(tmspan.Milliseconds / 10)));

Southwestwards

This is what I do. There really should be an easier way, that doesn't involve messing with ticks directly – Resurrectionist

Answer 6

My solution:

    static TimeSpan RoundToSec(TimeSpan ts)
    {
        return TimeSpan.FromSeconds((int)(ts.TotalSeconds));
    }

Klaraklarika

Indeed, truncation is easy. If you want to round, use Math.Round instead of (int), as I show in my first code snippet. – Epistrophe

Answer 7

Not sure about TimeSpan, but you might check this post on DateTimes:
http://mikeinmadison.wordpress.com/2008/03/12/datetimeround/

Behlau

Answer 8

Yet another way to round milliseconds to the nearest second.

private const long TicksPer1000Milliseconds = 1000 * TimeSpan.TicksPerMillisecond;

// Round milliseconds to nearest second
// To round up, add the sub-second ticks required to reach the next second
// To round down, subtract the sub-second ticks
elapsedTime = new TimeSpan(elapsedTime.Ticks + (elapsedTime.Milliseconds >= 500 ? TicksPer1000Milliseconds - (elapsedTime.Ticks % TicksPer1000Milliseconds) : -(elapsedTime.Ticks % TicksPer1000Milliseconds)));

Madea

Instead of TicksPer1000Milliseconds, I would call it TicksPerSeconds – Arabela

Answer 9

Here is a nice Extention-Method:

    public static TimeSpan RoundToSeconds(this TimeSpan timespan, int seconds = 1)
    {
        long offset = (timespan.Ticks >= 0) ? TimeSpan.TicksPerSecond / 2 : TimeSpan.TicksPerSecond / -2;
        return TimeSpan.FromTicks((timespan.Ticks + offset) / TimeSpan.TicksPerSecond * TimeSpan.TicksPerSecond);
    }

And here are some Examples:

DateTime dt1 = DateTime.Now.RoundToSeconds();  // round to full seconds
DateTime dt2 = DateTime.Now.RoundToSeconds(5 * 60);  // round to full 5 minutes

Curio

Answer 10

An extension method if you need to work with DateTime instead, but still want to round the time. In my case, I wanted to round to the minute.

public static DateTime RoundToMinute(this DateTime date)
    {
        return DateTime.MinValue.AddMinutes(Math.Round((date - DateTime.MinValue).TotalMinutes));
    }

Unstop

If you use "01. Jan. 2021, 23:59:50", what do expect as output? If my assumption is correct, you'll get "01. Jan. 2021, 00:00:00", which is wrong by almost 24 hours. It doesn't make sense to mix time and date here. – Matriarch

You're right, there was an error. I've fixed it. In my case, I really needed to round the moment in time, including the date to the minute. I agree that when it's not needed, it's easier to work only with the time. – Unstop