rand([maxNumber])

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rand([maxNumber])

rand()

rand

rand() returns a pseudo-random number between 0 and 1. No argument is required.

rand([maxNumber])

From v9.5.2, supplying an optional parameter maxNumber, which must be an integer, returns a random integer between 0 and maxNumber-1. This can be useful when wanting random list items, noting that list items are addressed using zero-based integers.

N.B. if working with list-based items, consider the List/Set.randomItem() operator (new to v9.5.2), which abstracts away the need to know the size of the list. Essentially it encapsulates calling list.at(rand(list.count)), so much easier to write/use

Getting 1-based ranges vs. zero-based ranges of values

Consider the original round() method:

$MyNumber=round(rand()*10); 

$MyNumber will be set to one of eleven integers in the range 0 through to 10. But, what if the '10' argument about is actually a child count:

$MyNumber=round(rand()*$ChildCount); 

If the $ChildCount was 10 and $MyNumber were used to fetch a random child using $SiblingOrder($MyNum) the process would fail if $MyNumber were zero as $SiblingOrder numbers from 1. Indeed, in this case the need is for ten integers, one through to ten.

Previously, 1-based range can be achieved:

$MyNumber=round(rand()*(10-1))+1; 

$MyNumber=round(rand()*($ChildCount-1))+1; 

If the main input is 10, by subtracting 1 the process returns a randomised integer in in the range 0-9 (ten numbers) and then adding back 1 shifts the value range to 1-10.

Using the newer rand(maxNumber) method the above becomes:

$MyNumber=round(rand($ChildCount-1))+1; 

This is why the List/Set.randomItem() may be an easier clear approach.