Random DateTime between range - not unified output

问题

I implemented the below RandomDate, but I always keep getting values closed to "From" date, i probably miss something here....

public static DateTime GetRandomDate(DateTime from, DateTime to)
    {
        var range = new TimeSpan(to.Ticks - from.Ticks);

        var rnd = new Random();

        var randTimeSpan = new TimeSpan((long)(range.TotalSeconds - rnd.Next(0, (int)range.TotalSeconds))); 

        return from + randTimeSpan;
    }

回答1:

You could change to:

static readonly Random rnd = new Random();
public static DateTime GetRandomDate(DateTime from, DateTime to)
{
    var range = to - from;

    var randTimeSpan = new TimeSpan((long)(rnd.NextDouble() * range.Ticks)); 

    return from + randTimeSpan;
}

Explanation: I used NextDouble() because it gives a number between 0.0 and 1.0. Your return value won't be a whole number of seconds in my solution. And I moved rnd out to a field on the class/struct. Because it's best to reuse one Random instance, and not create a new one every time one needs just one additional random number.

回答2:

The problem is that:

var randTimeSpan = new TimeSpan((long)(range.TotalSeconds - rnd.Next(0, (int)range.TotalSeconds)));

is creating a TimeSpan from TICKS, not from SECONDS.

You need:

var randTimeSpan = TimeSpan.FromSeconds((long)(range.TotalSeconds - rnd.Next(0, (int)range.TotalSeconds)));

(Please check the cast too - it needs to be a double passed to FromSeconds)

回答3:

This is because TimeSpan's constructor that takes a long expects ticks, not seconds.

var randTimeSpan = new TimeSpan(range.Ticks - rnd.Next(0, range.Ticks));

回答4:

Fixed ArgumentOutOfRangeException:

public static DateTime GetRandomDateTime(DateTime? min = null, DateTime? max = null)
{
    min = min ?? new DateTime(1753, 01, 01);
    max = max ?? new DateTime(9999, 12, 31);

    var range = max.Value - min.Value;
    var randomUpperBound = (Int32) range.TotalSeconds;
    if (randomUpperBound <= 0)
        randomUpperBound = Rnd.Next(1, Int32.MaxValue);

    var randTimeSpan = TimeSpan.FromSeconds((Int64) (range.TotalSeconds - Rnd.Next(0, randomUpperBound)));
    return min.Value.Add(randTimeSpan);
}

回答5:

This is working for me. The days interval is until 28 to avoid the exception with February.

Random r = new Random();
DateTime rDate = new DateTime(r.Next(1900, 2010), r.Next(1, 12), r.Next(1, 28));

回答6:

My idea is we just need some random number of ticks added to start datetime to get a random date in between start and end. So my solution does not create any TimeSpan objects.

private static readonly Random random = new Random ();
private static readonly object syncLock = new object ();

public static DateTime RandomDate(DateTime from, DateTime to)
{
    lock ( syncLock )
    {
         return from.AddTicks ((long) ( random.NextDouble () * ( to.Ticks - from.Ticks ) ));
    }
 }

来源：https://stackoverflow.com/questions/14505932/random-datetime-between-range-not-unified-output

标签

datetime

random

timespan