Is there a better way in C# to round a DateTime to the nearest 5 seconds?

Question

Hi all,

I want to round a DateTime to the nearest 5 seconds. This is the way I'm currently doing it but I was wondering if there was a better or more concise way?

DateTime now = DateTime.Now;
int second = 0;

// round to nearest 5 second mark
if (now.Second % 5 > 2.5)
{
    // round up
    second = now.Second + (5 - (now.Second % 5));
}
else
{
    // round down
    second = now.Second - (now.Second % 5);
}

DateTime rounded = new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute, second);

Please note that I've found these two previous questions, however they truncate rather than round the time.

Answer 1

Like you mentioned, it's fairly easy to truncate. So, just add 2.5 seconds, then truncate down.

Answer 2

The Ticks count of a DateTime represents 100-nanosecond intervals, so you can round to the nearest 5 seconds by rounding to the nearest 50000000-tick interval like this:

  DateTime now = DateTime.Now;
  DateTime rounded = new DateTime(((now.Ticks + 25000000) / 50000000) * 50000000);

That's more concise, but not necessarily better. It depends on whether you prefer brevity and speed over code clarity. Yours is arguably easier to understand.

Answer 3

I can't think of a better way, although I would probably factor out the round method:

static int Round(int n, int r)
{
    if ((n % r) <= r / 2)
    {
        return n - (n % r); 
    }
    return n + (r - (n % r));
}

Also, % returns an int, so comparing it to 2.5 strikes me as a little odd, even though it is correct. I'd use >= 3.

Answer 4

I couldn't recognize the difference between C# and a bar of soap but, if you're looking for a more concise solution, I would just put the whole thing in a function - there's little that will be more concise in your code than a call to said function:

DateTime rounded = roundTo5Secs (DateTime.Now);

Then you can put whatever you want in the function and just document how it works, such as (assuming these are all integer operations):

secBase = now.Second / 5;
secExtra = now.Second % 5;
if (secExtra > 2) {
    return new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute,
        secBase + 5);
}
return new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute,
    secBase);

You may also need some extra checks if secBase goes to 60 (unless C# DateTime objects are smart enough to bump up the minute (and hour if minute goes to 60, and so on).

Answer 5

How about this (blending a few answers together)? I think it conveys the meaning well and should handle the edge cases (rounding to the next minute) elegantly due to AddSeconds.

// truncate to multiple of 5
int second = 5 * (int) (now.Second / 5);
DateTime dt = new DateTime(..., second);

// round-up if necessary
if (now.Second % 5 > 2.5)
{
    dt = dt.AddSeconds(5);
}

The Ticks approach as shown by Jay is more concise, but may be a bit less readable. If you use that approach, at least reference TimeSpan.TicksPerSecond.