Generate a Random number between two ranges

Questions & Answers
1

Hi, so basically, the thing I need is to generate, for example a random number between two ranges…

For example from -15 to 15, but excepting, from -7 to 7… So, the accepted numbers would be: -15, -14, -13, -12, -11, -10, -9, -8, -7… 7, 8, 9, 10, 11, 12, 13, 14 and 15…

So, how can I do this using Random.Range? I want to get this number in a only call because I need it for a coordinate, for make object stay, not so far, but not so near…

Thanks in advance.

Bye.

3

Well, all you need is some simple math like this:

// C#
int num = Random.Range(7,25); // 7 .. 24 since 25 is exclusive.
if (num > 15)
    num = 9-num; // (9-16) .. (9-24) == -7 .. -15
// num == 7 .. 15 or -15 .. -7

edit
I have the feeling i should add some explanation. First of all you should figure out how many possible numbers you want to get in total. 7 to 15 and -15 to -7 are 9 values each. So there are 18 possible values. The Random.Range goes from 7 to 24 which has a range of 18 values. The lower 9 values is already our positive range (7 to 15) if we get a value larger then 15 we map the upper 9 values (16 to 24) down to (-7 to -15)

A more general approach could be something like this:

// C#
public struct Range
{
    public int min;
    public int max;
    public int range {get {return max-min + 1;}}
    public Range(int aMin, int aMax)
    {
        min = aMin; max = aMax;
    }
}

public static int RandomValueFromRanges(params Range[] ranges)
{
    if (ranges.Length == 0)
        return 0;
    int count = 0;
    foreach(Range r in ranges)
        count += r.range;
    int sel = Random.Range(0,count);
    foreach(Range r in ranges)
    {
        if (sel < r.range)
        {
            return r.min + sel;
        }
        sel -= r.range;
    }
    throw new Exception("This should never happen");
}

In this example the “Ranges” are max-inclusive. So in your case you would do:

int val = RandomValueFromRanges(new Range(-15,-7), new Range(7,15));

If you want the ranges to be max-exclusive you have to remove the “+1” in the range property. In this case you would have to do this to get the same result:

int val = RandomValueFromRanges(new Range(-15,-6), new Range(7,16));

Depending on your usecase when you want a relative offset with a min and max distance you would use a vector, a random direction and then just scale it between your min and max value.

public static Vector2 RandomXYOffset(float aMin, float aMax)
{
    float angle = Random.value * Mathf.PI * 2;
    Vector2 dir = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle));
    return dir * Random.Range(aMin, aMax);
}

The offset is of course not grid aligned but since you didn’t said your actual usecase we can only guess.

5

int rnd = Random.Range(7, 16) * (Random.Range(0, 2) == 0)? 1:-1;

4

A more versatile option would be to put all the random numbers in a data container (array or List). Then pick an int for the index

// Change this as appropriate
int[] numbers = new int[5] {1, 2, 3, 4, 5};

// Use this line to get a random number
int myRandom = numbers[Random.Range(0,numbers.length)];
2

Using your example, you could create a loop that gets a random number between -15 to 15, and then checks if the number is between -7 and 7. If it is between -7 and 7, you would get a new random number. Once a number is found that fits the qualifications, exit the loop.

As far as I’m aware, this is not possible in one call, unless you are lucky and get a number that works right away.
(“one call” meaning one Range call)

7

Hope this helps

int num= Random.Range(-15, 15);
        while((num > 0 && num < 7) || (num < 0 && num > -7))
        {
            num= Random.Range(-15, 15);
        }
6

You can do this:

int n1[2];
n1[0] = Random.Range(-15,-6);
n1[1] = Random.Range(7,16);

The random number —> n1[Random.Range(0,2)];