DateTime Round Up and Down

Question

Ive been looking for a proper rounding mechanism but nothing I find seems to be exactly what I need.

I need to round up and round down seperately and I also need to account for the the case when its already rounded.

I need the following rounding to happen

5:00 -> RoundDown() -> 5:00
5:04 -> RoundDown() -> 5:00
5:09 -> RoundDown() -> 5:00
5:10 -> RoundDown() -> 5:10

4:00 -> RoundUp() -> 4:00
4:50 -> RoundUp() -> 4:50
4:51 -> RoundUp() -> 5:00
4:56 -> RoundUp() -> 5:00 

Basically I need it to RoundUp() or RoundDown() to the nearest 10 minutes explicitly but it should also leave time untouched if it already is in a multiple of 10 minutes. Also I'd like to truncate any seconds to that they have no effect on the rounding procedure

4:50:45 -> 4:50:00 -> RoundUp() -> 4:50

Does anyone have any handy code to accomplish this.

I found this code somewhere but it rounds 5:00 -> RoundUp() -> 5:10 rather than leaving it intact because its already a multiple of 10 and needs no rounding. Also Im not sure how seconds would effect it

public static DateTime RoundDateTime(this DateTime dt, int minutes, RoundingDirection direction)
{
    TimeSpan t;
    switch (direction)
    {
        case RoundingDirection.Up:
            t = (dt.Subtract(DateTime.MinValue)).Add(new TimeSpan(0, minutes, 0)); break;
        case RoundingDirection.Down:
            t = (dt.Subtract(DateTime.MinValue)); break;
        default:
            t = (dt.Subtract(DateTime.MinValue)).Add(new TimeSpan(0, minutes / 2, 0)); break;
    }
    return DateTime.MinValue.Add(new TimeSpan(0,
           (((int)t.TotalMinutes) / minutes) * minutes, 0));
}

Hope someone can edit that method to make it work for me. Thanks

Mojave

Okay. So you have rounding code there. Why aren't you modifying it to make it do what you need to do? – Inexplicit

Would this work? #7029853 – Talbot

Your rounding rule is unclear. You round 5:09 to 5:00 but 4:56 to 5:00. – Dipteral

@Rawling: Um.. because 5:09 is being rounded down and 4:56 is being rounded up?? – Gamely

@mellam Oh gods I completely misread the question. Nothing to see here! (And picked the wrong example for how I read it anyway, I meant 4:51 to 5:00.) – Dipteral

Answer 1

How about:

case RoundingDirection.Up:
    t = dt.AddMinutes((60 - dt.Minute) % 10);
case RoundingDirection.Down:
    t = dt.AddMinutes(-dt.Minute % 10);

Demo: http://ideone.com/AlB7Q

Gamely

Does that take care of the seconds? – Talbot

Answer 2

This will let you round according to any interval given.

public static class DateTimeExtensions
{
  public static DateTime Floor(this DateTime dateTime, TimeSpan interval)
  {
    return dateTime.AddTicks(-(dateTime.Ticks % interval.Ticks));
  }

  public static DateTime Ceiling(this DateTime dateTime, TimeSpan interval)
  {
    var overflow = dateTime.Ticks % interval.Ticks;

    return overflow == 0 ? dateTime : dateTime.AddTicks(interval.Ticks - overflow);
  }

  public static DateTime Round(this DateTime dateTime, TimeSpan interval)
  {
    var halfIntervalTicks = (interval.Ticks + 1) >> 1;

    return dateTime.AddTicks(halfIntervalTicks - ((dateTime.Ticks + halfIntervalTicks) % interval.Ticks));
  }
}

To take care of truncating the seconds, I would simply subtract the seconds and milliseconds from the date-time before sending them into the rounding functions.

Styles

Answer 3

Here is a fast way to truncate (round down)

var now = DateTime.Now;
var nowTicks = now.Ticks;

//removing the nanoseconds, miliseconds, and seconds from the nowTicks
var lastMinute = new DateTime(nowTicks - (nowTicks % (1000*1000*10*60)));

Cowcatcher

Answer 4

This function will round up or down to the nearest interval (minutes).

    private static DateTime NormalizeReadingInterval(DateTime originalTime, int interval)
    {
        if (originalTime.Minute % interval == 0) return originalTime;
        var epochTime = new DateTime(1900, 1, 1);
        var minutes = (originalTime - epochTime).TotalMinutes;
        var numIntervals = minutes / interval;
        var roundedNumIntervals = Math.Round(numIntervals, 0);
        return epochTime.AddMinutes(roundedNumIntervals * interval);
    }

Nature

Answer 5

Another approach avoiding arithmetic using type long.

Using integer division, where a & b are positive integers:

a/b             // rounding down 
(a+b-1)/b       // rounding up 
((2*a)+b)/(2*b) // rounding to the nearest (0.5 up)

To round up:

public static DateTime UpToNearestXmin( DateTime dt, int block )
{
   int a = dt.Minute;
   int b = block;

   int mins = block * (( a + b - 1 ) / b );

   return new DateTime( dt.Year, dt.Month, dt.Day, dt.Hour, 0, 0 ).AddMinutes( mins );
}

To round down or to nearest, change the mins calculation as appropriate.

The minutes are rounded. The seconds & milliseconds are zeroed which is expected behaviour.

Koloski

Answer 6

Based on answer by @JasonS here is a solution that takes any type of TimeSpan as interval for rounding. e.g. every 15 minutes

public static DateTime RoundDown(this DateTime dt, TimeSpan nearestInterval)
{
    var rounded  = dt - TimeSpan.FromTicks(dt.Ticks % nearestInterval.Ticks);
  
    return rounded;
}

Orfinger