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Ben Nadel
On User Experience (UX) Design, JavaScript, ColdFusion, Node.js, Life, and Love.

Creating Random Dates in ColdFusion: RandDateRange( dtFrom, dtTo )

By Ben Nadel on
Tags: ColdFusion

Someone was just asking me how to create a random date in ColdFusion. More specifically, how to create a random date between two dates. The solutions for this is quite simple once you understand it. I have created a method named RandDateRange(). This method functions similar to RandRange( intFrom, intTo ) and actually uses that method under the hood. If you abstract generating a random date between two given dates, it comes down to picking a random point in time. We can create this random point by adding a random time span to the "From Date", making sure, of course, that this random time span does not give us a date past the desired "To Date".

The beauty of time spans in ColdFusion is that they can be represented as a single floating point number. This puts us in the perfect position to use RandRange() to create random time spans. To make sure that we do not create too large a timespan, our bottom range parameter will be zero and our top range parameter will be the difference in seconds between the two out lier dates. Therefore, if we get a random second value and add it to the "From Date", we know we can never go past the "To Date."

<cffunction name="RandDateRange" access="public" returntype="date" output="false"
	hint="This returns a random date between the two given dates (inclusive).">

	<!--- Define arguments. --->
	<cfargument name="FromDate" type="date" required="true" />
	<cfargument name="ToDate" type="date" required="true" />

	<cfscript>

		// Define the local scope.
		var LOCAL = StructNew();

		// Get the difference in seconds between the two dates.
		LOCAL.TimeDifference = DateDiff(
			"s",
			ARGUMENTS.FromDate,
			ARGUMENTS.ToDate
			);

		// Create a random time increment based on the second difference.
		// The time span object is a representation of time-length in
		// terms of a single floating-point number.
		LOCAL.TimeIncrement = CreateTimeSpan(
			0, // Days
			0, // Hours
			0, // Minutes
			RandRange( // Seconds
				// Our smallest possible time increment.
				0,

				// Our largest possible time increment that will not
				// put us past the ToDate.
				LOCAL.TimeDifference
				)
			);

		// Get a new random date based on the FromDate and the random
		// time span.
		LOCAL.RandomDate = (ARGUMENTS.FromDate + LOCAL.TimeIncrement);

		// This random date now is formatted like a TimeSpan object,
		// meaning that it is in the form of one floating point number.
		return( LOCAL.RandomDate );

	</cfscript>
</cffunction>

Now to test it out. For the from and to dates, let's pick Now and one month from Now.

From: 2006-07-07
To: 2006-08-07

Now, get a random date between those to:

Random: 38931.4080093

As you can see above, the random date is in Time Span format (represented as a single floating point number). In order to fix that, all we have to do is run a date format on it. Now, keep in mind that ColdFusion still treats that as a valid date. You only need to change the formatting on it for display. You can add, diff, subtract all you want on the server side and its all good.

Formatted: 2006-08-02



Reader Comments

Nice!

Thanks for this, nice, tightly coded function that worked straight off the page. Integrated into a site in five minutes. You sire, are a champ.

Thanks
Shaun