Generate a random date between two other dates

Question

How would I generate a random date that has to be between two other given dates?

The function's signature should something like this:

randomDate("1/1/2008 1:30 PM", "1/1/2009 4:50 AM", 0.34)
                  ^                       ^          ^

           date generated has   date generated has a random number
           to be after this     to be before this

and would return a date such as: 2/4/2008 7:20 PM

Answer 1

In python:

>>> from dateutil.rrule import rrule, DAILY
>>> import datetime, random
>>> random.choice(
                 list(
                     rrule(DAILY, 
                           dtstart=datetime.date(2009,8,21), 
                           until=datetime.date(2010,10,12))
                     )
                 )
datetime.datetime(2010, 2, 1, 0, 0)

(need python dateutil library – pip install python-dateutil)

Answer 2

What do you need the random number for? Usually (depending on the language) you can get the number of seconds/milliseconds from the Epoch from a date. So for a randomd date between startDate and endDate you could do:

1. compute the time in ms between startDate and endDate (endDate.toMilliseconds() - startDate.toMilliseconds())
2. generate a number between 0 and the number you obtained in 1
3. generate a new Date with time offset = startDate.toMilliseconds() + number obtained in 2

Answer 3

Pandas + numpy solution

import pandas as pd
import numpy as np

def RandomTimestamp(start, end):
    dts = (end - start).total_seconds()
    return start + pd.Timedelta(np.random.uniform(0, dts), 's')

dts is the difference between timestamps in seconds (float). It is then used to create a pandas timedelta between 0 and dts, that is added to the start timestamp.

Answer 4

A tiny version.

import datetime
import random


def random_date(start, end):
    """Generate a random datetime between `start` and `end`"""
    return start + datetime.timedelta(
        # Get a random amount of seconds between `start` and `end`
        seconds=random.randint(0, int((end - start).total_seconds())),
    )

Note that both start and end arguments should be datetime objects. If you've got strings instead, it's fairly easy to convert. The other answers point to some ways to do so.

Answer 5

Since Python 3 timedelta supports multiplication with floats, so now you can do:

import random
random_date = start + (end - start) * random.random()

given that start and end are of the type datetime.datetime. For example, to generate a random datetime within the next day:

import random
from datetime import datetime, timedelta

start = datetime.now()
end = start + timedelta(days=1)
random_date = start + (end - start) * random.random()

Answer 6

Conceptually it's quite simple. Depending on which language you're using you will be able to convert those dates into some reference 32 or 64 bit integer, typically representing seconds since epoch (1 January 1970) otherwise known as "Unix time" or milliseconds since some other arbitrary date. Simply generate a random 32 or 64 bit integer between those two values. This should be a one liner in any language.

On some platforms you can generate a time as a double (date is the integer part, time is the fractional part is one implementation). The same principle applies except you're dealing with single or double precision floating point numbers ("floats" or "doubles" in C, Java and other languages). Subtract the difference, multiply by random number (0 <= r <= 1), add to start time and done.